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Products => Test Equipment => Topic started by: motocoder on July 11, 2015, 06:18:22 pm

Title: Economical option for precision frequency reference?
Post by: motocoder on July 11, 2015, 06:18:22 pm
I picked  up an HP 53131A a while back. After fixing a few small issues, the thing seems to be working great. However, this one came with the low-end oscillator. I've ordered an OCXO for it (off eBay), and when that comes in, I'd like to calibrate it.

I've read through a number of threads on this topic, and I see people have Rubidium frequency references, and GPS-disciplined references. On the GPS option, I see there are some surplus units that used to be inexpensive, but now the price is creeping up. Also, I am not sure what exactly is needed there.
But what I'd really like is if someone can give me some practical suggestions on what is the most practical way to set up a good frequency reference - what is needed, and what's the best place to source one.

Thanks!
Title: Re: Economical option for precision frequency reference?
Post by: mazurov on July 11, 2015, 06:54:33 pm
If you need one-time setting of coarse adjustment of the unit you can cobble up a manual gpsdo from a GPS module with 1pps output like the one Adafruit carries plus PIC32 micro clocked from the unit being calibrated. You can PLL input clock of the micro to 50 MHz and then count between GPS 1PPS pulses. Using this technique I was able to get a HP 10544A within less tan 10 Hz on couple occasions.
Title: Re: Economical option for precision frequency reference?
Post by: Lightages on July 11, 2015, 07:02:50 pm
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263 (http://www.ebay.com/itm/281701995263)
I have no experience with this unit nor the seller but it looks good.

Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7 (http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7)
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 11, 2015, 07:24:53 pm
The answer really depends on the precision you want.  The following are in increasing order of cost / complexity / performance.

1.  Zero-beat the OCXO against WWV at 10 MHz.  Requires a 10 MHz shortwave receiver.  Maybe 1 Hz accuracy.

2.  Measure the carrier frequency of WWVB at 60 KHz.  Requires a tuned LC circuit / antenna and amplifier for 60 KHz.  Maybe 0.1 Hz.

Now you jump to accuracy levels in the 1e-9 to 1e-12 level.

3.  Rb standard.  Assumes that the unit is working and has been calibrated against a known standard.  Drift is in the range of 5e-11 per month.  Jitter isn't an issue.

4.  Bare GPS receiver.  Measure the output frequency.  Usually 1 PPS although some units have an auxiliary output with a programmable frequency.  Requires a decent antenna location.  No drift.  Jitter will be in the range of 5 - 100 ns rms depending on which unit you get.  Make sure you get a timing GPS rather than a navigation GPS.  Navigation GPS units can have 1 PPS jitter in the microsecond range.

5.  GPSDO.  Requires a decent antenna location.  No drift.  Jitter is < 1 ns rms.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 11, 2015, 08:52:52 pm
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263 (http://www.ebay.com/itm/281701995263)
I have no experience with this unit nor the seller but it looks good.

Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7 (http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7)
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.

The GPS option there looks good. I wonder if anyone here has any experience with that unit, though. I'm a bit leary about buying something from China with no confirmation that it's not junk.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 11, 2015, 08:56:09 pm
The answer really depends on the precision you want.  The following are in increasing order of cost / complexity / performance.

1.  Zero-beat the OCXO against WWV at 10 MHz.  Requires a 10 MHz shortwave receiver.  Maybe 1 Hz accuracy.

2.  Measure the carrier frequency of WWVB at 60 KHz.  Requires a tuned LC circuit / antenna and amplifier for 60 KHz.  Maybe 0.1 Hz.

Now you jump to accuracy levels in the 1e-9 to 1e-12 level.

3.  Rb standard.  Assumes that the unit is working and has been calibrated against a known standard.  Drift is in the range of 5e-11 per month.  Jitter isn't an issue.

4.  Bare GPS receiver.  Measure the output frequency.  Usually 1 PPS although some units have an auxiliary output with a programmable frequency.  Requires a decent antenna location.  No drift.  Jitter will be in the range of 5 - 100 ns rms depending on which unit you get.  Make sure you get a timing GPS rather than a navigation GPS.  Navigation GPS units can have 1 PPS jitter in the microsecond range.

5.  GPSDO.  Requires a decent antenna location.  No drift.  Jitter is < 1 ns rms.

This is a great list. I really want something that I don't have to periodically recalibrate. There's a window right where I would want to place a GPSDO, so I don't think antenna location will be an issue. So given that, a GPSDO seems like the way to go.

Any suggestions on options for that? What about the unit that Lightages posted a link to in the thread above? From the pictures in the listing, it looks like it is using a GPS chip intended for navigation (uBlox NEO-6M). Data sheet on that is here:

https://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf (https://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf)
Title: Re: Economical option for precision frequency reference?
Post by: blueskull on July 11, 2015, 09:28:51 pm
I have an old X72 Rb clock, which is rated for 20 years operation, and it has been ran for about 8 years. I would say it will run happily for another at least 5 years. Currently it locks in 40 seconds.

Also, I have 2 new old stock stratum 3 20Mhz OCXOs from CTS.

If you are interested in them, please PM me a price you want to pay for one or all of them.

I am currently in Raleigh, NC, and I ship to any lower 48 states.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 11, 2015, 10:21:37 pm
This is a great list. I really want something that I don't have to periodically recalibrate. There's a window right where I would want to place a GPSDO, so I don't think antenna location will be an issue. So given that, a GPSDO seems like the way to go.

Any suggestions on options for that? What about the unit that Lightages posted a link to in the thread above? From the pictures in the listing, it looks like it is using a GPS chip intended for navigation (uBlox NEO-6M). Data sheet on that is here:

https://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf (https://www.u-blox.com/images/downloads/Product_Docs/NEO-6_DataSheet_(GPS.G6-HW-09005).pdf)

Remember that recalibration intervals are related to required accuracy.  If you have a calibrated Rb standard that drifts at 5e-11 per month, and your accuracy needs are only (!) 1 ppb, you only have to recalibrate every 20 months.  Maybe not a problem.

The BG7TBL GPSDO has been evaluated here:  http://www.ke5fx.com/gpscomp.htm (http://www.ke5fx.com/gpscomp.htm) .  It puzzles me a little.  Based on the graphs, it isn't performing as well as the other GPSDOs that I'm familiar with.  Using the NEO-6M would have an effect, but that's not enough to explain the performance.

However, due to a happy coincidence, there is another option.  I suggest you look at this one:  http://www.ebay.com/itm/221777430088 (http://www.ebay.com/itm/221777430088) .  Since it's on sale, the price is very close to the BG7TBL unit.  With names like Lucent and Symmetricom behind it, you know it's going to be good!  There was a long discussion on this unit on the Time-Nuts mailing list some months ago.  Lots of reverse-engineering and info.  The mailing list archive is here:  https://www.febo.com/pipermail/time-nuts/ (https://www.febo.com/pipermail/time-nuts/) .

Title: Re: Economical option for precision frequency reference?
Post by: Electro Fan on July 11, 2015, 10:36:40 pm
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263 (http://www.ebay.com/itm/281701995263)
I have no experience with this unit nor the seller but it looks good.

Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7 (http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7)
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.

The GPS option there looks good. I wonder if anyone here has any experience with that unit, though. I'm a bit leary about buying something from China with no confirmation that it's not junk.


I think member TSL has experience either with the GPSDO unit or a similar unit - I think he did some extensive testing.  Maybe he will surface and see this - he is very experienced with precise clocking.
Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on July 11, 2015, 11:48:06 pm
Quote
2.  Measure the carrier frequency of WWVB at 60 KHz.  Requires a tuned LC circuit / antenna and amplifier for 60 KHz.  Maybe 0.1 Hz.

That's the best all round option IMO in terms of cost, speed and reliability. I tried testing a similar cheap and cheerful circuit for 198kHz (BBC Droitwich, UK) some time ago and got very good results with just a simple antenna, amplifier and a hard limiter chip. All of the above can be built very quickly from surplus parts for next to zero cost. The performance wasn't as good as my old homebrew offair standard but it was good enough :)

When used with a reciprocal counter it should completely outclass the GPSDO and Rb options in terms of cost and speed/convenience to calibrate as you should be able to get a good result in less than 1 minute from cold. Obviously, the offair std isn't as accurate as a well settled GPSDO but I can't think of a valid reason why I'd need the extra accuracy because nothing I have here in terms of test gear or things I've designed can maintain better accuracy over a few months than the simple offair standard can deliver when averaged over a few minutes.

Note:

I've got a (Jackson Labs?) GPSDO here inside some comms equipment and apart from powering up the GPSDO module once to see how painfully slow it is to lock up and how much of a PITA it is to deploy the antenna outside I haven't used it since. I think I've had it here several months now.

By comparison, a simple LF offair standard can lock and be useful in about 1 minute from cold and it runs on flea power and can be placed anywhere in the house :)





Title: Re: Economical option for precision frequency reference?
Post by: Electro Fan on July 12, 2015, 12:00:23 am
 a quick Google search found these:

http://www.leapsecond.com/pages/sony-wwvb/ (http://www.leapsecond.com/pages/sony-wwvb/)

http://www.joejaworski.com/wwvb/ (http://www.joejaworski.com/wwvb/)

https://www.sparkfun.com/products/retired/10060 (https://www.sparkfun.com/products/retired/10060)

- maybe someone can post some better info/instructions for building something
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 12, 2015, 12:11:18 am
If you're going to use WWVB (or similar low frequency broadcast) you don't really want one of the 'atomic' clocks.  They decode the signal and give you time of day.  But typically, the carrier frequency is locked to an atomic clock, while the modulation may not be.  As a result, any signal derived from the clock information may not be as stable as the carrier itself.

What you need is the RF carrier frequency (i.e. 60 KHz).  You need to ignore or filter out whatever modulation is present.  So you use a 60 KHz tuned RF circuit (maybe a ferrite rod), coil, and tuning capacitor plus an amplifier / limiter to boost the signal and block out the modulation.  I've seen various web sites that talk about this, but can't come up with any links right now.

Title: Re: Economical option for precision frequency reference?
Post by: PaulAm on July 12, 2015, 12:49:20 am
The GPSDO that Edpalmer42 mentioned is down to $100 which is $25 less than when I bought one.

That's got to be the best deal around at the moment.  It's NOS still in the original packing containers.  Add a power supply, an antenna and you're good to go.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 12, 2015, 04:14:42 am
The GPSDO that Edpalmer42 mentioned is down to $100 which is $25 less than when I bought one.

That's got to be the best deal around at the moment.  It's NOS still in the original packing containers.  Add a power supply, an antenna and you're good to go.

For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?

Edpalmer42 - thanks for the recommendations. I may also do some experiments with WWV, but I'd like to get the GPSDO working first.
Title: Re: Economical option for precision frequency reference?
Post by: Wuerstchenhund on July 12, 2015, 11:12:10 am
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263 (http://www.ebay.com/itm/281701995263)
I have no experience with this unit nor the seller but it looks good.

I have this one, and while I haven't cross-checked it with another source I'm sure it does what it says on the tin, although as described at http://www.ke5fx.com/gpscomp.htm (http://www.ke5fx.com/gpscomp.htm) it doesn't seem to run at exactly 10MHz but 9.9999999998MHz instead.

The main reason I went for this instead of an used HP/Agilent or whatever GPS disciplined OCXO were price, the absence of need for modification before use, and that it's rather compact and not in some odd slot-in module format with backplane connector. I did replace the GPS antenna that came with the unit with a better one which gives me better receiption, though.
Title: Re: Economical option for precision frequency reference?
Post by: jpb on July 12, 2015, 12:23:38 pm
If you can set a long gate time on the counter and it measures low frequencies (1Hz) then you can check a 10MHz OCXO by using it as a reference and measuring the 1pps from a cheap (£30) GPS module.

I did this with my TF930 counter. Of course you need to do it over a long time as there is quite a lot of jitter  from pulse-to-pulse.

The module I use is this one from Adafruit as it has an external antenna and is quite an accurate one ( 10nsecs according to the spec sheet - others are up to 50 nsecs or more):

http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/ (http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/)

The other method is to use a scope, use the 1pps to trigger the scope and observe the phase shift on the 10MHz (assuming the phase shift is less than the 100 nsec period which it should be).
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 12, 2015, 04:35:19 pm
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?

Any good quality power supply should be fine.  People tend to prefer linear supplies for frequency references, but since most of the commercial units have internal switching supplies I don't think it makes much difference.  It looks like each of the two units needs 24V at 2 amps.  You don't have to run both units - remember that this was for Lucent who always specifies redundant systems - but it's probably best to start with both to make sure everything is working properly.

Any 5 volt GPS antenna will work.  Some of the newer antennas are 3.3 volt only so look carefully.  However, you'll get the best performance with a timing-grade antenna.  They typically have narrower filtering than navigation antennas. Just search for <gps antenna timing> and start browsing.

The antenna should be mounted outdoors with a clear view of the sky towards the equator (since that's the direction where you'll see more satellites).  You may be able to get away with an indoor antenna, but it will definitely reduce the signal levels and the number of satellites tracked.  It may cause the unit to lose lock and go into holdover.  More gain is better.  These older GPSDOs tend to have poorer sensitivity than current ones.  This could become an issue if you have a long cable run from the antenna to the receiver.  In the manual for the Trimble Thunderbolt they recommend RG-59 or RG-6 cable between the antenna and the receiver.  They basically say "Yes, we know it's 75 ohms and the equipment is 50 ohms.  It doesn't matter.  The cable is good, cheap, and widely available.  Shut up and use it!"  ... or words to that effect.  :)

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 12, 2015, 11:06:35 pm
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?

Any good quality power supply should be fine.  People tend to prefer linear supplies for frequency references, but since most of the commercial units have internal switching supplies I don't think it makes much difference.  It looks like each of the two units needs 24V at 2 amps.  You don't have to run both units - remember that this was for Lucent who always specifies redundant systems - but it's probably best to start with both to make sure everything is working properly.

Any 5 volt GPS antenna will work.  Some of the newer antennas are 3.3 volt only so look carefully.  However, you'll get the best performance with a timing-grade antenna.  They typically have narrower filtering than navigation antennas. Just search for <gps antenna timing> and start browsing.

The antenna should be mounted outdoors with a clear view of the sky towards the equator (since that's the direction where you'll see more satellites).  You may be able to get away with an indoor antenna, but it will definitely reduce the signal levels and the number of satellites tracked.  It may cause the unit to lose lock and go into holdover.  More gain is better.  These older GPSDOs tend to have poorer sensitivity than current ones.  This could become an issue if you have a long cable run from the antenna to the receiver.  In the manual for the Trimble Thunderbolt they recommend RG-59 or RG-6 cable between the antenna and the receiver.  They basically say "Yes, we know it's 75 ohms and the equipment is 50 ohms.  It doesn't matter.  The cable is good, cheap, and widely available.  Shut up and use it!"  ... or words to that effect.  :)

I'm not worried about the cable. I have my ham radio AE license, and used to tinker around with radios, so I should have some good 50 ohm coax around.

Thanks for the tips on the PS and antenna. I can probably find a 24V dongle on eBay, and will look for an antenna with the criteria you suggest.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 12, 2015, 11:07:27 pm
If you can set a long gate time on the counter and it measures low frequencies (1Hz) then you can check a 10MHz OCXO by using it as a reference and measuring the 1pps from a cheap (£30) GPS module.

I did this with my TF930 counter. Of course you need to do it over a long time as there is quite a lot of jitter  from pulse-to-pulse.

The module I use is this one from Adafruit as it has an external antenna and is quite an accurate one ( 10nsecs according to the spec sheet - others are up to 50 nsecs or more):

http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/ (http://proto-pic.co.uk/ultimate-gps-breakout-66-channel-w-10-hz-updates-mtk3339-chipset/)

The other method is to use a scope, use the 1pps to trigger the scope and observe the phase shift on the 10MHz (assuming the phase shift is less than the 100 nsec period which it should be).

That sounds like a good way to double-check the reference as well. Thanks
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 13, 2015, 11:01:24 pm
For $100, I think I'll give it a go. It seems like it will be a fun project to get that up and working. Any suggestions on PS and Antenna?

Any good quality power supply should be fine.  People tend to prefer linear supplies for frequency references, but since most of the commercial units have internal switching supplies I don't think it makes much difference.  It looks like each of the two units needs 24V at 2 amps.  You don't have to run both units - remember that this was for Lucent who always specifies redundant systems - but it's probably best to start with both to make sure everything is working properly.

Any 5 volt GPS antenna will work.  Some of the newer antennas are 3.3 volt only so look carefully.  However, you'll get the best performance with a timing-grade antenna.  They typically have narrower filtering than navigation antennas. Just search for <gps antenna timing> and start browsing.

The antenna should be mounted outdoors with a clear view of the sky towards the equator (since that's the direction where you'll see more satellites).  You may be able to get away with an indoor antenna, but it will definitely reduce the signal levels and the number of satellites tracked.  It may cause the unit to lose lock and go into holdover.  More gain is better.  These older GPSDOs tend to have poorer sensitivity than current ones.  This could become an issue if you have a long cable run from the antenna to the receiver.  In the manual for the Trimble Thunderbolt they recommend RG-59 or RG-6 cable between the antenna and the receiver.  They basically say "Yes, we know it's 75 ohms and the equipment is 50 ohms.  It doesn't matter.  The cable is good, cheap, and widely available.  Shut up and use it!"  ... or words to that effect.  :)

Any thoughts on either of these antennas (i think they might be the same, barring the read color of the collar)?

http://www.ebay.com/itm/NIB-Lucent-PCTEL-GPS-TMG-HR-26NCM-26dB-Timing-Antenna-N-f-w-Collar-Mount-MaxRad-/301687250710?pt=LH_DefaultDomain_0&hash=item463df61f16 (http://www.ebay.com/itm/NIB-Lucent-PCTEL-GPS-TMG-HR-26NCM-26dB-Timing-Antenna-N-f-w-Collar-Mount-MaxRad-/301687250710?pt=LH_DefaultDomain_0&hash=item463df61f16)
http://www.ebay.com/itm/Datum-2640NW-D-E-GPS-26dB-5V-Antenna-Telecom-Timing-N-Conn-PCTEL-Lucent-NEW-/361230143301?pt=LH_DefaultDomain_0&hash=item541afe8f45 (http://www.ebay.com/itm/Datum-2640NW-D-E-GPS-26dB-5V-Antenna-Telecom-Timing-N-Conn-PCTEL-Lucent-NEW-/361230143301?pt=LH_DefaultDomain_0&hash=item541afe8f45)

I would also need to source a cable with the correct connectors. I have some cable, but not with these connectors on them. Looks like I would need a TNC male on one end and an N male on the other.

Title: Re: Economical option for precision frequency reference?
Post by: Lightages on July 13, 2015, 11:08:39 pm
I decided to get the unit I posted earlier from ebay. It should make a nice video when I get back to making videos.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 13, 2015, 11:43:05 pm
I decided to get the unit I posted earlier from ebay. It should make a nice video when I get back to making videos.

I am looking forward to seeing that.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 18, 2015, 09:27:27 am
Heres my 2 cents worth.
After installing a High Stability Timebase Option (clone) for my 53131a I needed to calibrate it some how. I tried zero beating WWV's carrier but I quickly learned about the varying propagation delay caused by the variation of the ionosphere and receiving WWVH at the same time gave me too much error so my brother suggested using a GPS Disciplined Clock as a reverence source. The last time that I looked the cost was just way too much for me. Just recently I found the prices were getting reasonable so I purchased a Trimble Thunderbolt. After the 30 day warranty ran out it started to reboot on occasion so I found the BG7TBL GPSDO from China and decided what the hell, I will get one. I must admit, the build quality was pretty impressive and I liked the small size so I picked up 2 more as backups lol. With the el-cheapo supplied antenna placed on the north side of the house (north is bad) it tracks 12 birds most of the time. Just for giggles I stuck a resistor in the antenna connector and to my surprise it tracked 4 birds ! 

Screen shot of the BG7TBL:
 
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 18, 2015, 09:28:13 pm
Here are the results of my tests on my Lucent RFTG-u GPSDO.

The first picture shows the phase measurements between the GPSDO and my Efratom FRT Rb standard.  For comparison, I've also shown the same measurement with my HP Z3801A GPSDO.  It's much better to measure phase - i.e. time interval - than frequency difference because frequency measurement implies averaging over a period of time or requires unobtainable accuracy while phase difference is a relatively simple measurement.  Also, many counters measure time interval much more accurately than frequency.  Odd, but true.  The graph shows that the RFTG-u is much busier than the Z3801A, but is otherwise working properly.  I don't know whether it will settle down over time or can be tweaked.  Most GPSDOs don't allow you to modify the parameters of the internal control loops.  The Trimble Thunderbolt is a notable exception.

The second picture shows the Allan Deviation results for both measurements.  If you're not familiar with Allan Deviation, it's the standard calculation used to evaluate the noise and stability of any kind of oscillator.  The math is beyond me, but I think I've got the operational basics figured out.

In these graphs, the X-axis value represents measurement duration or interval between measurements while the Y-axis represents stability or resolution.  For example, if you make a measurement that's one second long, your resolution can't be better than 3.6e-11.  If you extend that to 10 seconds with the Z3801A, you can resolve to about 4e-12.  The RFTG-u is noisier at 10 seconds, so your resolution will be 6e-12.  If you get into the underlying mathematics you'll find that my explanation isn't quite right, but it's good enough for now.

But wait, that's still not right!  Each graph is actually a composite measurement.  The measurement system, the device under test (the RFTG-u) and the reference (the FRT) all contribute to the graph.  At any point along the X-axis, the graph represents the combination of the three elements.  Typically, it represents the performance of the worst of the three at that point in time.

In my graphs, the straight-line segment on the left of the graph represents the limitations of my measurement system.  It's only when the graph deviates from a straight line that you see the performance of the oscillators inside the GPSDOs.  Hopefully, as time passes, the oscillator in the RFTG-u will settle down and the relatively flat section of the graph will drop lower, perhaps dropping as far as the Z3801A graph or beyond.

But just after the oscillators have started to show their worth, they run into the 'GPS line'.  That's my name for it.  It represents the approximate performance limit of the GPS system.  The oscillators are forced to turn and follow that line.  Every GPSDO will do the same thing.  Sometimes one side of the line, sometimes the other.  It will vary from unit to unit and maybe data run to data run.  Normally, the oscillator would continue toward the upper right of the graph as aging became significant so, in this case, the graph isn't really showing the worst of the three elements.

So where's the FRT in this explanation?  It's stability is good enough that it hasn't made an appearance yet.  It's running lower than the other elements in the test so it's not visible.  If I ran the test longer, both graphs would start to rise as the aging of the FRT became significant.  The upwards hook on the end of the black graph might be the FRT, but the end of these graphs flap around quite dramatically so you can't be sure.  This characteristic is inherent in the mathematics involved and doesn't represent a deficiency in the equipment, the measurement, or the calculations.

The software used to collect this data and generate the graphs is called Timelab, an excellent, freeware, open source program written and actively supported by John Miles and available from http://www.ke5fx.com/timelab/readme.htm (http://www.ke5fx.com/timelab/readme.htm) .

Ed

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 19, 2015, 12:01:21 am
Heres my 2 cents worth.
After installing a High Stability Timebase Option (clone) for my 53131a I needed to calibrate it some how. I tried zero beating WWV's carrier but I quickly learned about the varying propagation delay caused by the variation of the ionosphere and receiving WWVH at the same time gave me too much error so my brother suggested using a GPS Disciplined Clock as a reverence source. The last time that I looked the cost was just way too much for me. Just recently I found the prices were getting reasonable so I purchased a Trimble Thunderbolt. After the 30 day warranty ran out it started to reboot on occasion so I found the BG7TBL GPSDO from China and decided what the hell, I will get one. I must admit, the build quality was pretty impressive and I liked the small size so I picked up 2 more as backups lol. With the el-cheapo supplied antenna placed on the north side of the house (north is bad) it tracks 12 birds most of the time. Just for giggles I stuck a resistor in the antenna connector and to my surprise it tracked 4 birds ! 

Screen shot of the BG7TBL:

I think it's a good option. I may end up with one of these at some point, but it will be fun to get the Lucent unit running.
Title: Re: Economical option for precision frequency reference?
Post by: George_Race on July 19, 2015, 01:25:53 am
Not sure what reasonable price is to you, but for $250 you can have a primary standard in your shop.
For several years I have been using a Trimble Thunderbolt GPS.  I have it driving the 10 MHz external standard input of 2 frequency counters, my HP Signal Generator, My HP Spectrum Analyzer, and other stuff on my work bench.
And this is considered a PRIMARY STANDARD!  Precise frequency generation and measurements can be made to .01 Hz time and time again.

Here is a complete unit, including a 10 MHz distribution amplifier for $250!
Click on the link below:
http://www.ebay.com/itm/TRIMBLE-GPS-RECEIVER-THUNDERBOLT-KIT-DISTRIBUTION-AMP-/291515708632?pt=LH_DefaultDomain_0&hash=item43dfb0b4d8 (http://www.ebay.com/itm/TRIMBLE-GPS-RECEIVER-THUNDERBOLT-KIT-DISTRIBUTION-AMP-/291515708632?pt=LH_DefaultDomain_0&hash=item43dfb0b4d8)

There is a lot of information on the web concerning the use of the Trimble Thunderbolt as a primary standard.   Do some searching and a lot of info will pop up.
If you are interested, I can send a lot more information on what I put together to get the job done.
Hope this helps,
George - WB8BGY

Look at the bottom picture on this page.  It shows my Trimble Thunderbolt information.  Running the Lady Heather program on an old laptop.

http://www.mrrace.com/product_pages/other_items/MyTestBench/index.htm (http://www.mrrace.com/product_pages/other_items/MyTestBench/index.htm)

73...George
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 19, 2015, 05:12:38 pm
However, due to a happy coincidence, there is another option.

Thanks for the heads up on the Lucent/Symmetricom, I pulled the trigger and now am in GPSDO land.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 19, 2015, 05:48:35 pm
Crap, wish I didnt see the Lucent/Symmetricom but for that price I had to pull the trigger to  |O
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 19, 2015, 06:20:27 pm
Just been reading up on them quite interesting. I thought what no 10MHz! Then I realized they were talking about the GPS receiver which has 10MHz on the PCB, just no external connector. $100 for 5, 10 and 15MHz, 1pps, time/date, redundancy, interface. What more could you ask for?

You could probably go around to a friends place leave him the redundant unit working then go home and use the receiver.

http://www.febo.com/pipermail/time-nuts/2014-October/087274.html (http://www.febo.com/pipermail/time-nuts/2014-October/087274.html)
Title: Re: Economical option for precision frequency reference?
Post by: PaulAm on July 19, 2015, 07:51:54 pm
I just picked up a NOS Lucent timing antenna with mount for $30.  Now waiting for an N/F adapter so I can put it on the roof.  Still have to throw a power supply together and gut an ancient UPS in a half rack cabinet to put it in.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 20, 2015, 04:15:19 pm
I just picked up a NOS Lucent timing antenna with mount for $30.  Now waiting for an N/F adapter so I can put it on the roof.  Still have to throw a power supply together and gut an ancient UPS in a half rack cabinet to put it in.

Think I have a similar one that came with my Nortel Trimble NTGS50AA unit. Dont notice much difference in performance between it and the el-cheapo $5 Chinese ones.

73 
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 20, 2015, 05:14:33 pm
Just been reading up on them quite interesting. I thought what no 10MHz! Then I realized they were talking about the GPS receiver which has 10MHz on the PCB, just no external connector. $100 for 5, 10 and 15MHz, 1pps, time/date, redundancy, interface. What more could you ask for?

You could probably go around to a friends place leave him the redundant unit working then go home and use the receiver.

http://www.febo.com/pipermail/time-nuts/2014-October/087274.html (http://www.febo.com/pipermail/time-nuts/2014-October/087274.html)

Yes, it seems like a great deal. Mine arrived on Saturday. I ordered the wrong cable (got a RP-TNC instead of TNC, and I need to rig up some sort of a DB9 connector for power), so I wasn't able to hook it up. However, looking at the construction of this thing, it is obviously a serious quality piece of gear.

Looking forward to getting it running this weekend.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 20, 2015, 07:48:45 pm
Just been reading up on them quite interesting. I thought what no 10MHz! Then I realized they were talking about the GPS receiver which has 10MHz on the PCB, just no external connector. $100 for 5, 10 and 15MHz, 1pps, time/date, redundancy, interface. What more could you ask for?

You could probably go around to a friends place leave him the redundant unit working then go home and use the receiver.

http://www.febo.com/pipermail/time-nuts/2014-October/087274.html (http://www.febo.com/pipermail/time-nuts/2014-October/087274.html)

Yes, it seems like a great deal. Mine arrived on Saturday. I ordered the wrong cable (got a RP-TNC instead of TNC, and I need to rig up some sort of a DB9 connector for power), so I wasn't able to hook it up. However, looking at the construction of this thing, it is obviously a serious quality piece of gear.

Looking forward to getting it running this weekend.

Isn't J1 the 10Mhz out pictured on the bottom unit ?
I tried looking for more info info on these units and suspect thats why they are cheap because theres practically NO information on these units  :scared:
I think I read in that one article that the power goes straight into a DC/DC converter so thats where I am going to feed mine.
Looks like your the 1st kid on the block with one of these old-timers so PLEASE keep us posted with your finding. 

73
Good luck ! 
Title: Re: Economical option for precision frequency reference?
Post by: dadler on July 21, 2015, 01:24:50 am
Economical is a very relative term. Something like this is ready to go:
http://www.ebay.com/itm/281701995263 (http://www.ebay.com/itm/281701995263)
I have no experience with this unit nor the seller but it looks good.

Another option is this:
http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7 (http://www.ebay.com/itm/FEI-fe-5680b-rubidium-oscillator-With-1pps-20mhz-output-ONLY-10mhz-NEED-to-MOD-/291419889143?pt=LH_DefaultDomain_0&hash=item43d9fa9df7)
I purchased one from this seller and have modified it to output 10MHz. It was only a handful of cheap parts to do so. The information is mentioned in his auction. If you need cheaper than $65, then the options get rather few.

I ordered one of the "needs to be modified" FE-5680B units from the eBay link you provided above.

Just received it--it came with a DB15/VGA connector. Did yours have a VGA connector?
Title: Re: Economical option for precision frequency reference?
Post by: Lightages on July 21, 2015, 03:01:33 am
Actually I think it is called an HD15 connector. Yes that is how mine came.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 21, 2015, 04:31:52 am
Looks like your the 1st kid on the block with one of these old-timers so PLEASE keep us posted with your finding. 

Was my message on the previous page too long for you?   >:(

Here's the condensed version:

It works.
The longer you let it run, the better it works.

The end.

Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 21, 2015, 06:17:09 am
Pinouts for the Lucent/Symmetricom Z3811A Z3812A (use at your own risk)
http://www.febo.com/pipermail/time-nuts/2014-October/087674.html (http://www.febo.com/pipermail/time-nuts/2014-October/087674.html)

Some software made by the late Ulrich Bangert, that you might find useful, made compatible (see readme) for the Lucent/Symmetricom Z3811A Z3812A.
http://www.nc7j.com/downloads/ng7m/Time-Nuts/Z38XX-Modified-for-Lucent-Z3811A-Z3812A/readme.txt (http://www.nc7j.com/downloads/ng7m/Time-Nuts/Z38XX-Modified-for-Lucent-Z3811A-Z3812A/readme.txt)
http://www.nc7j.com/downloads/ng7m/Time-Nuts/Z38XX-Modified-for-Lucent-Z3811A-Z3812A/Z38XX.zip (http://www.nc7j.com/downloads/ng7m/Time-Nuts/Z38XX-Modified-for-Lucent-Z3811A-Z3812A/Z38XX.zip)

A Frequency Doubler and Distribution Amplifier by Gerhard W. Hoffmann
http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf (http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf)

HP/Agilent/Keysight product page
http://www.keysight.com/en/pd-Z3810AS%3Aepsg%3Apro-pn-Z3810AS/gps-timing-system?cc=GW&lc=eng (http://www.keysight.com/en/pd-Z3810AS%3Aepsg%3Apro-pn-Z3810AS/gps-timing-system?cc=GW&lc=eng)
Discontinued product document
http://www.keysight.com/upload/cmc_upload/All/Disco_Products_not_on_site.pdf (http://www.keysight.com/upload/cmc_upload/All/Disco_Products_not_on_site.pdf)

HP says this product was sold to Symmetricom, who is now owned by Microsemi.
The Z3811A Z3812A are made to Lucents KS24361 standard to operate with their mobile equipment.

If anyone has success finding more or specific manuals/schematics for the Z3811A Z3812A please let us know.

===============

There is some Lucent RFTG (comparison use only) info on the ko4bb.com website, search for "RFTG".

User guide for the Z3801 (comparison use only).
http://www.leapsecond.com/museum/z3801a/097-z3801-01-iss-1.pdf (http://www.leapsecond.com/museum/z3801a/097-z3801-01-iss-1.pdf)
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 21, 2015, 06:31:49 am
Yes, Ulrich's program, Z38XX, works quite well.  Other than the initial recognition, it doesn't seem to have any problem with the RTFG.

Be careful when you're searching for info on the RFTG.  There were two versions that were rather different from each other.  The one we're talking about includes two OCXOs.  The other version had one OCXO and a Rubidium standard.  Internally, the two versions are quite different.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 21, 2015, 06:45:27 am
Yes, Ulrich's program, Z38XX, works quite well.  Other than the initial recognition, it doesn't seem to have any problem with the RTFG.

Be careful when you're searching for info on the RFTG.  There were two versions that were rather different from each other.  The one we're talking about includes two OCXOs.  The other version had one OCXO and a Rubidium standard.  Internally, the two versions are quite different.

Ed

Yes exactly don't go reading about a 9 pin connector and blow yours up or trash the firmware or config somehow, there is a certain level of competency required and that includes not making assumptions.

Ed do you have the Z3811A Z3812A or any other info on them?
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 21, 2015, 03:31:23 pm
Ed do you have the Z3811A Z3812A or any other info on them?

Yes, I have the Z3811A / Z3812A pair aka Z3810AS aka KS-24361 aka RFTG-u.  ::)  I bought them a few months ago for a spare.  My tests shown earlier in this thread were done on that pair.

Unfortunately, the only info we have is whatever you can figure out or others have figured out.  The best source is the Time-Nuts mailing list.

FYI, here's some of the info that Z38xx shows when hooked up to the Z3811AS.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 21, 2015, 03:34:16 pm
This is a really interesting thread, but finding it pretty difficult to determine what models are being referenced during each post. (hard to follow). Describing a model using "it" without a prior mention of exactly what "it" is,  is really confusing. Thunderbolts, RFTG, RFTG-u, Z3810, Z3811, etc., etc., etc...  giving the model # in each post, helps alot, rather than trying to dig through the whole thread trying to figure that out. I currently have here an RFTG (Rb/GPSDO/OCXO), an RFTG-u system with (2) REF0 units, and (1) REF1 unit, (including the Lucent 15 pin Hi Density Xover cable), an RFG-Rb, several decent 10mHz OCXOs, and (3) Stanford Research FS700s . So many clocks, so little time... :)
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 23, 2015, 05:39:37 am
Does anyone have contacts at HP/Agilent/Keysight, Symmetricom/Microsemi or Lucent/Alcatel-Lucent (before Nokia buys it out) who could get a guy in tech support or sales to dig up the Z3811A / Z3812A pair (Z3810AS) specific documentation? e.g. operation/programming/service manuals

It's a bit expensive for me to get on the phone and get through to the right support from here but I'm certain someone there in the US can dig up the manuals or get hold of the correct person to speak to. Perhaps an installer or servicer might have documentation as well.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 23, 2015, 06:44:25 am
Does anyone have contacts at HP/Agilent/Keysight, Symmetricom/Microsemi or Lucent/Alcatel-Lucent (before Nokia buys it out) who could get a guy in tech support or sales to dig up the Z3811A / Z3812A pair (Z3810AS) specific documentation? e.g. operation/programming/service manuals

It would be wonderful if someone could find such documentation.  In the meantime, all members of the Z38xx family speak the same language.  I have a Z3801A and the manual is available online for it.  But I found that the command section of the Z3805A manual (also available online) was more useful.  Between these two documents, the Z38XX program from Ulrich Bangert that can talk to almost all the Z38xx units as well as a few others, and the reverse-engineering efforts of the members of the Time-Nuts mailing list, we've got quite a lot of info on a unit that was never intended to be publicly available.

Ed

Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 24, 2015, 07:02:35 pm
The HP 70310A Precision Frequency Reference is a Slot module that was available for the 70004A / 70001A MMS systems...
Included a PLL, but only an OCXO (by Corning) driving it. capability to lock an external ref as well. HP sold em' for around $5K, an interesting item 10mHz, 100mHz out with Distr. Amp option.  Power Supply for the modules is a 40kHz bus around 27 VRMS. OCXO uses 20VDC. Look on the bay.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 01:54:51 am
edpalmer42 -

I finally powered  up the two Lucent units today. I just have the antenna hooked up indoors, but I thought I'd see how things look. I have the interface cable connected between the two units, and 24V applied from a switching adapter that can supply 3.75A.

When it powers on, it cycles through all 4 LEDs, and then goes into a state with the "NO GPS" and  "FAULT" LEDs lit. Is that normal? I am going to leave it on and see if the state changes, but I wanted to make sure there isn't some issue with these units.

Oh! While I typed this, the REF0 unit LEDs have changed. Now they say "NO GPS" and "ON" - no other lights. REF1 lights are the same - "NO GPS" and "FAULT"
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 02:42:44 am
Sounds about right.  I forget exactly what happens, but the lights dance around for a while.  At this point, the GPS is pulling one way, the OCXO is pulling another way, and the poor little micro is just totally confused.  Give it an hour or two to gain some semblance of sanity.  Once the GPS figures out where it is and the OCXO properly warms up, things will start to settle down and you'll see the 'On' light on Ref 0 and the 'Stby' light on Ref 1 both on solid.  If you don't have an RS422 adapter, use the hack described in the first message on the Time-Nuts mailing list.  Get the unit hooked up to a PC so you can see what's happening.  I recommend you use the modified Z38xx program.  It includes some data collection functions so you can track the performance of the unit.  Ultimately, the performance will be dependant on just how good your particular OCXO is and how carefully written the software was.

The picture below shows some of the things Z38xx can show.  You open up each of these views under the View tab on the main screen.

The top left graph shows the number of satellites locked and the Holdover Uncertainty Prediction (HUP).  I like the HUP.  The unit is estimating how far off it would be if it lost all satellites for 24 hours.  The value here is okay, but not great.  My Z3801A moves between about 3.5 us and < 0.5 us.  As the OCXO improves, this should drop.  Less than 1 us is really good.

The top right graph shows the error between the 1 PPS and GPS in blue and the EFC voltage to the OCXO in red.  The way the EFC is bouncing around explains the relatively high HUP and the jumpiness of the 1 PPS.  Hopefully, as the OCXO works the kinks out after its long nap, it will settle down and start showing a smooth graph that slopes either up or down and just runs straight.  This could take 30 days or more.  Although I don't see it on the datasheet, many OCXOs specify 30 days of continuous operation before they meet their aging specs.  Some really high precision units specify at least 90 days.  The longer it runs, the better it will perform.  It's best to leave it running permanently.  The unit's ultimate performance will be determined by your particular OCXO and the design parameters of the software.

The bottom left chart shows the signal strength of each satellite.  If your view of the sky isn't great, or your antenna or cabling isn't very good, you'll see it here.

The bottom right screen is the status report from the unit.  You could run Hyperterm or putty and get this with the command :SYST:STAT? .  It might be a good idea to start with a program like that just to ensure that your communications are working properly.

I won't bother posting another graph of the Allan Deviation.  It has improved some, but until the OCXO settles down, the results aren't particularly meaningful.  Even so, the results shown earlier are good.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 03:27:05 am
Fault lights are gone, but still no GPS lock. The relatively insensitive receiver in these older units may not be able to pick up the signal indoors. I may have to figure out how to run a cable outside.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 03:30:38 am
Don't worry about the antenna until you get Z38xx running.  Without it, you're flying blind.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 25, 2015, 03:47:50 am
I have been trying to get the Z38XX to run but having no luck and looks like my REF1 unit took a dump today, doesnt seem to be receiving anything anymore, yellow GPS light just stays on now. It was working yesterday (excepts the com prog.)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 04:24:52 am
Don't worry about the antenna until you get Z38xx running.  Without it, you're flying blind.

Ed

Ok, I have a USB RS-422 adapter, but I will probably have to do some surgery to get the cable pinout correct. Have you seen any source that gives the pinout for that?

Thanks for posting the detail above - that is really useful.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 05:44:20 am
I have been trying to get the Z38XX to run but having no luck and looks like my REF1 unit took a dump today, doesnt seem to be receiving anything anymore, yellow GPS light just stays on now. It was working yesterday (excepts the com prog.)

Keep working on Z38xx.  Until you can talk to the box, there's very little you can troubleshoot.  Are you using an RS-422 converter or the hack?

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 06:16:32 am
I have been trying to get the Z38XX to run but having no luck and looks like my REF1 unit took a dump today, doesnt seem to be receiving anything anymore, yellow GPS light just stays on now. It was working yesterday (excepts the com prog.)

Keep working on Z38xx.  Until you can talk to the box, there's very little you can troubleshoot.  Are you using an RS-422 converter or the hack?

Ed

I am using an RS422 converter from Gearmo, and two DB9 breakout connectors and some wires to correct the cable pinout. It's a bit of a hack, but I've got that working now. The main issue I was having was that I had it connected to J6 instead of J8   :palm:

So, good news is, I can run the :SYST:STAT? command you gave me. Bad news is, it doesn't appear to be tracking any satellites at all. The antenna is indoors, but it's right next to a window. The window faces East.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 06:51:31 am
Is :SYST:STAT? reporting a time of day or a location, in particular, wrong ones?  I don't know how much you know about GPS, but the receiver has to find at least one bird to get the date and time and then download the almanac & ephemeris data before it can start to find the other birds.  It's amazing that it can do it at all.  If it already has a location stored, iti'll be looking for the wrong birds in the wrong directions and it'll take a very long time to sort itself out.  You might be able to help it out by giving it a date, time, and location.  There are commands for that in the manual for the Z3801A or 58503A (aka Z3816A - yes more alternate names).  Remember that all these boxes have the same basic command structure.

Or, just let it run and see if magic happens.  It sometimes looks hopeless, but then you turn away and when you look back, it's done!

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 06:59:22 am
Is :SYST:STAT? reporting a time of day or a location, in particular, wrong ones?  I don't know how much you know about GPS, but the receiver has to find at least one bird to get the date and time and then download the almanac & ephemeris data before it can start to find the other birds.  It's amazing that it can do it at all.  If it already has a location stored, iti'll be looking for the wrong birds in the wrong directions and it'll take a very long time to sort itself out.  You might be able to help it out by giving it a date, time, and location.  There are commands for that in the manual for the Z3801A or 58503A (aka Z3816A - yes more alternate names).  Remember that all these boxes have the same basic command structure.

Or, just let it run and see if magic happens.  It sometimes looks hopeless, but then you turn away and when you look back, it's done!

Ed

This is what :SYST:STAT? is reporting:

-------------------------- Secondary Receiver Status --------------------------
SYNCHRONIZATION ............................ [ Outputs Valid/Reduced Accuracy ]
SmartClock Mode ___________________________   Reference Outputs _______________
>> Locked to Ext: stabilizing frequency       TFOM     3             FFOM     1
   Recovery                                   1PPS TI -50.0 ns relative to Ext
   Holdover                                   HOLD THR 1.000 us
   Power-up                                   Holdover Uncertainty ____________
                                              Predict  432.0 us/initial 24 hrs

ACQUISITION ................................................ [ Ext 1PPS Valid ]
Tracking: 0 ____   Not Tracking: 8 ________   Time ____________________________
                   PRN  El  Az                GPS      06:56:19 (?) 25 Jul 2015
                   * 1  -- ---                GPS 1PPS Invalid: not tracking
                   * 3  -- ---                ANT DLY  60 ns
                   *11  -- ---                Position ________________________
                   *12  -- ---                MODE     Survey:      0% complete
                   *13  -- ---                         Suspended: track <4 sats
                   *18  -- ---                INIT LAT     0:00:00.000
                   *26  -- ---                INIT LON     0:00:00.000
                   *29  -- ---                INIT HGT           +0.00 m  (GPS)
ELEV MASK 10 deg   *attempting to track
HEALTH MONITOR ......................................................... [ OK ]
Self Test: OK    Int Pwr: OK   Oven Pwr: OK   OCXO: OK   EFC: OK   GPS Rcv: OK
E-113>


Also, while trying to copy that to the clipboard, I inadvertently pasted it back in the terminal window. Now the prompt I am receiving says "E-101>" instead of "E-113>". Any idea what that means? I'm worried that I changed some setting...

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 07:21:04 am
Ignore my last question about the prompt. I found the manual for the Z3801A, and based on that got the commands to set the time (which I assume is in UTC), and the Lat/Long for my location. So let's see how things go now.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 07:42:00 am
This doesn't look too bad.

Notice that it's got the date and time right, even though it's not quite sure it believes it.  That means that it did receive at least one satellite.  As Dave would say:  "There's a trap for young players."  The time isn't UTC.  It's GPS time.  GPS Time doesn't pay any attention to leap seconds so it's currently 17 seconds ahead of UTC.  There is a command to change from GPS Time to UTC Time but it's not in the manual.  Google for it.

It may or may not have been able to download all the data it wants.  It obviously hasn't tracked enough birds simultaneously to calculate its location.  Since you've now given it your approximate location, it should speed up the process.  Until it's finished the initial acquisition, you can't even tell if your signal strength is going to be acceptable or not.

See where it talks about 'Mode: Survey' ?  After it finds the birds, it goes into a survey mode where it figures out its exact location.  I forget how long that takes.  Then it changes to 'Mode: Hold' .  That's when it can really start to lock down the OCXO.  Of course, at that point, the OCXO is still probably staggering around like a drunken sailor so the control is not entirely effective.  ;)  The HUP will stay at 432 us (its default value) for some hours, at least, and then start to come down.  Mine is still staggering around.

By the way, don't forget that 'staggering around' means that over the last three days my unit has deviated from perfection by less than 300 parts per billion so for most normal purposes, it's perfectly usable.  The error of the 10 MHz signal would be less than 1 Hz.  Yes, I'm a Time-Nut.  :)

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 08:08:49 am
This doesn't look too bad.

Notice that it's got the date and time right, even though it's not quite sure it believes it.  That means that it did receive at least one satellite.  As Dave would say:  "There's a trap for young players."  The time isn't UTC.  It's GPS time.  GPS Time doesn't pay any attention to leap seconds so it's currently 17 seconds ahead of UTC.  There is a command to change from GPS Time to UTC Time but it's not in the manual.  Google for it.

It may or may not have been able to download all the data it wants.  It obviously hasn't tracked enough birds simultaneously to calculate its location.  Since you've now given it your approximate location, it should speed up the process.  Until it's finished the initial acquisition, you can't even tell if your signal strength is going to be acceptable or not.

See where it talks about 'Mode: Survey' ?  After it finds the birds, it goes into a survey mode where it figures out its exact location.  I forget how long that takes.  Then it changes to 'Mode: Hold' .  That's when it can really start to lock down the OCXO.  Of course, at that point, the OCXO is still probably staggering around like a drunken sailor so the control is not entirely effective.  ;)  The HUP will stay at 432 us (its default value) for some hours, at least, and then start to come down.  Mine is still staggering around.

By the way, don't forget that 'staggering around' means that over the last three days my unit has deviated from perfection by less than 300 parts per billion so for most normal purposes, it's perfectly usable.  The error of the 10 MHz signal would be less than 1 Hz.  Yes, I'm a Time-Nut.  :)

Ed

I diddled around with the antenna location, and disconnected it several times. I wonder if I should restart the survey.

BTW - I noticed when I gave it the command to set the time that it set the time ahead of the value I gave it, so I suspect it is set to take the time in UTC and it converted it to GPS time.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 25, 2015, 10:14:24 am
Regarding not using an antenna, can GPSDOs or specifically the Z3811A, RFTG-U REF-1 units be run without the antenna while testing it and setting up the RS422? or can damage occur running it this way?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 02:04:25 pm
It ran all night, checked this morning - still not tracking any satellites. So either that eBay antenna is broken or  its just not sensitive enough to pick up any satellites indoors.

This may be a deal killer for me. I'm not sure I want to go through all the hassle of setting up an outdoor antenna.
Title: Re: Economical option for precision frequency reference?
Post by: SeanB on July 25, 2015, 02:22:46 pm
tried by a south facing window? my cheapie gps works with it sitting on the sill inside, facing north west.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 02:25:30 pm
tried by a south facing window? my cheapie gps works with it sitting on the sill inside, facing north west.

I have seen several GPS, including the one in my phone, work indoors here. However, those all use newer, more sensitive GPS chips.

The houses are very close together here. There is a house blocking the view of the sky on the south-facing window.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 02:28:49 pm
I diddled around with the antenna location, and disconnected it several times. I wonder if I should restart the survey.

BTW - I noticed when I gave it the command to set the time that it set the time ahead of the value I gave it, so I suspect it is set to take the time in UTC and it converted it to GPS time.

I don't think it's necessary to restart the survey.  If it loses satellites, it just suspends the survey until it sees more and then it resumes where it left off.  Is the survey still at 0%?  If it's > 0%, that means that it did get a reasonable fix sometime through the night and started the survey.  If so, is the location still exactly what you entered?

It didn't 'convert' the time to GPS.  It assumed that the time you gave it was GPS, but then it managed to receive a satellite signal and updated its time to the time that it got from the bird.

Quote
It ran all night, checked this morning - still not tracking any satellites. So either that eBay antenna is broken or  its just not sensitive to pick up any satellites indoors.

This may be a deal killer for me. I'm not sure I want to go through all the hassle of setting up an outdoor antenna.

Before you give up, try to get your antenna temporarily to a better location.  Tie it to a broom and stick it out the window so that it can see towards the equator if you have to.  Don't forget that you want to point the antenna up.   ;)  What antenna have you got?

A GPSDO does require a reasonable antenna.  I'm on the top floor of an apartment building.  I was able to get an adequate signal with a timing-grade antenna indoors but since I was able to, I moved the antenna outdoors and now I've got a great signal.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 02:37:00 pm
I diddled around with the antenna location, and disconnected it several times. I wonder if I should restart the survey.

BTW - I noticed when I gave it the command to set the time that it set the time ahead of the value I gave it, so I suspect it is set to take the time in UTC and it converted it to GPS time.

I don't think it's necessary to restart the survey.  If it loses satellites, it just suspends the survey until it sees more and then it resumes where it left off.  Is the survey still at 0%?  If it's > 0%, that means that it did get a reasonable fix sometime through the night and started the survey.  If so, is the location still exactly what you entered?

It didn't 'convert' the time to GPS.  It assumed that the time you gave it was GPS, but then it managed to receive a satellite signal and updated its time to the time that it got from the bird.

Quote
It ran all night, checked this morning - still not tracking any satellites. So either that eBay antenna is broken or  its just not sensitive to pick up any satellites indoors.

This may be a deal killer for me. I'm not sure I want to go through all the hassle of setting up an outdoor antenna.

Before you give up, try to get your antenna temporarily to a better location.  Tie it to a broom and stick it out the window so that it can see towards the equator if you have to.  Don't forget that you want to point the antenna up.   ;)  What antenna have you got?

A GPSDO does require a reasonable antenna.  I'm on the top floor of an apartment building.  I was able to get an adequate signal with a timing-grade antenna indoors but since I was able to, I moved the antenna outdoors and now I've got a great signal.

Ed

Survey still at 0%, location has not changed.

Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on July 25, 2015, 02:54:15 pm
Meanwhile, in much less time than it takes to type this post I connected a counter to a ferrite loop antenna + amplifier/filter + hard limiter circuit and was able to see 198.000000kHz +/- 0.000001kHz from BBC Radio 4 on an old Philips reciprocal counter on a 10 second gate time. The counter is connected to a decent OCXO that should be within about 0.02Hz at 10MHz.

i.e it takes maybe 30 seconds to get this resolution/agreement of 1mHz in 198kHz and confirm that the counter is seeing a stable signal on a 10 second gate time.

Nothing needs to 'lock' nothing needs to stagger about and the above lashup will work anywhere in the house. OK, maybe if I sat it next to a wallwart battery charger it might not work due to the RFI from a charger but it will realistically give a decent result in way less than 1 minute from cold anywhere in the house with no need for an external antenna.

How much more accuracy do you need?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 03:14:48 pm
Meanwhile, in much less time than it takes to type this post I connected a counter to a ferrite loop antenna + amplifier/filter + hard limiter circuit and was able to see 198.000000kHz +/- 0.000001kHz from BBC Radio 4 on an old Philips reciprocal counter on a 10 second gate time. The counter is connected to a decent OCXO that should be within about 0.02Hz at 10MHz.

i.e it takes maybe 30 seconds to get this resolution/agreement of 1mHz in 198kHz and confirm that the counter is seeing a stable signal on a 10 second gate time.

Nothing needs to 'lock' nothing needs to stagger about and the above lashup will work anywhere in the house. OK, maybe if I sat it next to a wallwart battery charger it might not work due to the RFI from a charger but it will realistically give a decent result in way less than 1 minute from cold anywhere in the house with no need for an external antenna.

How much more accuracy do you need?

Thanks for the comment. We've gone well beyond the bounds of "need" here.

Back to the topic at hand, I think the pole I had the antenna on, which was sitting in teh window sill, may have been putting the antenna in a really bad spot (blocked by the window frame). At least that's my theory. I fashioned a crude mount for the antenna, so that it can rest stably at the *bottom* of the window, which is where I was able to get a GPS lock on other devices.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 03:16:31 pm
And, that made a big difference. Tracking 2 satellites now.
Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on July 25, 2015, 03:34:48 pm
Realistically, you need to deply the GPS antenna outside with a decent view of the sky. A few years ago I borrowed a Quartzlock E8-Y GPSDO from work to review it.

http://quartzlock.com/product/frequency-reference/gps/E8-Y (http://quartzlock.com/product/frequency-reference/gps/E8-Y)

I found it would declare it was locked after about 45minutes even with an indoor antenna sat by a window (like you have done).
But the performance was nowhere near as good as it should be. It flashes LEDs to say how many satellites it is tracking and even with several satellites it delivered relatively poor frequency stability with the window antenna. Much worse than I can get with the above 198kHz offair lashup.

But once I put the antenna outside and it could see a fair bit of sky it performed a lot better. However, I could still get it to misbehave just by moving the unit or rotating it.

Basically, it just isn't worth the hassle. I'm not alone in this view at my place of work. I'm not aware of ANY engineer who actually uses this E8-Y as a 10MHz reference in the labs at work. The old school Quartzlock 198kHz offair standards are much preferred because they are portable anywhere within the building and work within about 1 minute and deliver enough performance to calibrate a decent OCXO in our designs or in a piece of test gear.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 03:46:28 pm
Meanwhile, in much less time than it takes to type this post I connected a counter to a ferrite loop antenna + amplifier/filter + hard limiter circuit and was able to see 198.000000kHz +/- 0.000001kHz from BBC Radio 4 on an old Philips reciprocal counter on a 10 second gate time. The counter is connected to a decent OCXO that should be within about 0.02Hz at 10MHz.

i.e it takes maybe 30 seconds to get this resolution/agreement of 1mHz in 198kHz and confirm that the counter is seeing a stable signal on a 10 second gate time.

Nothing needs to 'lock' nothing needs to stagger about and the above lashup will work anywhere in the house. OK, maybe if I sat it next to a wallwart battery charger it might not work due to the RFI from a charger but it will realistically give a decent result in way less than 1 minute from cold anywhere in the house with no need for an external antenna.

How much more accuracy do you need?

Excellent question!  And one that each user needs to answer.  At the beginning of this thread I gave a list of options.  Decide where you need or want to be on that list and go from there.

For 'normal' users, zero-beating against an HF station or using one of the LF stations as you've described might be the perfect solution.

There are ham operators who operate at 10 GHz.  They need to be within a few Hertz of the correct frequency to contact the other end so they probably need accuracy of 1e-9 or even better.  If you're a space hobbyist who's trying to pick up signals from deep space, 1e-9 might be so bad that your equipment is broken!

If you're a time-nut like me, need has very little to do with it.  You want to see how far you can push things.  A while ago, I bought a dead Cesium Frequency Standard.  I tested the tube to see if it had any life left in it.  I was able to measure the frequency of the response peak as 9.192 631 790 GHz.  Curses!  My calibration was 20 Hz off!  I should have measured .... 770, not ....790.  ;D

By the way, when I said that my 'staggering around' system was within 300 parts per billion, I was wrong.  I made a silly mistake.  Now that I've had some sleep I looked at the numbers again and found that the frequency error of the 10 MHz is around .001 Hz or 0.1 parts per billion.  In fact, that's likely the limit of my measurement system.  Making measurements at these levels is always an issue!

Ed
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 25, 2015, 03:55:17 pm
Realistically, you need to deply the GPS antenna outside with a decent view of the sky. A few years ago I borrowed a Quartzlock E8-Y GPSDO from work to review it.

http://quartzlock.com/product/frequency-reference/gps/E8-Y (http://quartzlock.com/product/frequency-reference/gps/E8-Y)

I found it would declare it was locked after about 45minutes even with an indoor antenna sat by a window (like you have done).
But the performance was nowhere near as good as it should be. It flashes LEDs to say how many satellites it is tracking and even with several satellites it delivered relatively poor frequency stability with the window antenna. Much worse than I can get with the above 198kHz offair lashup.

But once I put the antenna outside and it could see a fair bit of sky it performed a lot better. However, I could still get it to misbehave just by moving the unit or rotating it.

Basically, it just isn't worth the hassle. I'm not alone in this view at my place of work. I'm not aware of ANY engineer who actually uses this E8-Y as a 10MHz reference in the labs at work. The old school Quartzlock 198kHz offair standards are much preferred because they work within about 1 minute and deliver enough performance to calibrate a decent OCXO in our designs or in a piece of test gear.

I'm not familiar with the Quartzlock products, but I've often thought of GPSDOs and precision quartz oscillators as 'Prima Donnas'.  They can be incredible performers, but any little thing can throw them off.  If you need or want this level of performance, you accomodate their eccentricities.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 09:26:10 pm
It will occasionally list a satellite as tracking, but it quickly drops it, and now it's been running for almost 24 hours with zero progress on teh survey. Looks like this thing is a nonstarter unless I'm willing to drill holes in the wall and run a cable to an outside antenna. I wish I had realized that, as I'm sure that other unit on eBay, using a modern GPS chip, would have no issues pulling in the sats.

Anyone interested in buying this, PM me.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on July 25, 2015, 09:36:45 pm
Pm sent, i might give it a try.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 25, 2015, 10:27:59 pm
What puzzles me is that if you read the original Time Nuts mailing list post on these things, the author describes using a "poorly-sited indoor GPS antenna", and yet his system apparently completed the survey in a few hours. Something is wrong here. I am wondering if the antenna I got off of eBay is broken.

Can someone recommend an antenna that is known to work well with this unit?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 12:11:35 am
Sorry for the thread spam, just updating all the details in case anyone else gets one of these. I am not a big fan of mailing lists because the archives are really hard to search for useful info. I like this site, and searching past threads has helped me numerous times. So I think it's good to capture some of this data here.

I got the wife to help me set up the antenna outside. It's still on that wood block I mounted it on earlier this morning; the whole thing is just resting on the ground about 10 feet from my window. But it immediately, upon power-up, started tracking 4 satellites, and now it's up to 6. So a huge improvement.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 12:17:31 am
Woo hoo! Status now says:

"Locked to GPS: stabilizing frequency"

And the NO GPS light is no longer lit.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 12:55:45 am
Wow, even located outside it is having some issues. The survey has now been suspended because it no longer has 4 satellites tracking. Really piss-poor GPS in this thing, I guess. I guess I'll  have to get the antenna up on the roof to use it.
Title: Re: Economical option for precision frequency reference?
Post by: DarthBubba on July 26, 2015, 01:09:44 am
Okay, it looks like my message didn't "take."  Must've been the oversized .PDF I attached.

Greetings again!  I've recently purchased a Symmetricom X72 Rubidium reference oscillator for frequency-standard purposes.  I'd like to know if anyone here can point me to a GPSDO to use for nudging this thing to stay on-frequency, or, does anyone here offer services to sync it back to 10MHz?  From reading here it'll not need re-syncing for about two years.  I tried to attach the reference .PDF, but it's too big for this system.

Thanks in advance.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 26, 2015, 01:39:49 am
Wow, even located outside it is having some issues. The survey has now been suspended because it no longer has 4 satellites tracking. Really piss-poor GPS in this thing, I guess. I guess I'll  have to get the antenna up on the roof to use it.

What signal strengths are you seeing for the satellites?  How do they compare to the screen capture I posted back on page 4?  I have a VIC-100 Timing Antenna with about 38 db gain + 100 ft. of RG-59 coax (about 11 db loss @ 1.5 GHz) plus a few couplers and short cables, so call it 25 db gain to the receiver.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 02:22:04 am
Wow, even located outside it is having some issues. The survey has now been suspended because it no longer has 4 satellites tracking. Really piss-poor GPS in this thing, I guess. I guess I'll  have to get the antenna up on the roof to use it.

What signal strengths are you seeing for the satellites?  How do they compare to the screen capture I posted back on page 4?  I have a VIC-100 Timing Antenna with about 38 db gain + 100 ft. of RG-59 coax (about 11 db loss @ 1.5 GHz) plus a few couplers and short cables, so call it 25 db gain to the receiver.

Ed

Ed, I don't have that software set up yet - just the serial terminal. Do you know how to see that data via the console interface?

I will go back in the thread and see if I can find the link to that software and get that set up.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 02:31:03 am
Wow, even located outside it is having some issues. The survey has now been suspended because it no longer has 4 satellites tracking. Really piss-poor GPS in this thing, I guess. I guess I'll  have to get the antenna up on the roof to use it.

What signal strengths are you seeing for the satellites?  How do they compare to the screen capture I posted back on page 4?  I have a VIC-100 Timing Antenna with about 38 db gain + 100 ft. of RG-59 coax (about 11 db loss @ 1.5 GHz) plus a few couplers and short cables, so call it 25 db gain to the receiver.

Ed

Here's a screen capture of the signal strength window. I'm not sure what units those are - something proportional to dBm I suspect. Looks like my signals are not as good. Looks like you are farther north than me, so I don't think it's my latitude. Maybe antenna, the adapters I have on both ends of the cable, or the coax itself.

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 26, 2015, 02:53:57 am
Here's a screen capture of the signal strength window. I'm not sure what units those are - something proportional to dBm I suspect. Looks like my signals are not as good. Looks like you are farther north than me, so I don't think it's my latitude. Maybe antenna, the adapters I have on both ends of the cable, or the coax itself.

Those levels are just fine.  C/N stands for carrier to noise level.  I don't remember what the reference is.  Levels above 50 are unusually good.  Above 40 is good.  Above 30 is okay.  You'll find that those levels will change from satellite to satellite and if there are any trees or buildings around, the level from a particular satellite will change as it moves across the sky and is either blocked or has multipath problems.

You should do just fine with those signals.  I didn't notice how long mine took to do the survey.  I'm guessing it was only a few hours at most.  If it has to stop and start the survey, it will obviously take longer.  I have an absolutely clear view of the sky from east to south to west so it has no problem here.

By the way, that same signal level info is in the output of the :SYST:STAT command.  That's where Z38xx gets it from.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 03:27:08 am
Here's a screen capture of the signal strength window. I'm not sure what units those are - something proportional to dBm I suspect. Looks like my signals are not as good. Looks like you are farther north than me, so I don't think it's my latitude. Maybe antenna, the adapters I have on both ends of the cable, or the coax itself.

Those levels are just fine.  C/N stands for carrier to noise level.  I don't remember what the reference is.  Levels above 50 are unusually good.  Above 40 is good.  Above 30 is okay.  You'll find that those levels will change from satellite to satellite and if there are any trees or buildings around, the level from a particular satellite will change as it moves across the sky and is either blocked or has multipath problems.

You should do just fine with those signals.  I didn't notice how long mine took to do the survey.  I'm guessing it was only a few hours at most.  If it has to stop and start the survey, it will obviously take longer.  I have an absolutely clear view of the sky from east to south to west so it has no problem here.

By the way, that same signal level info is in the output of the :SYST:STAT command.  That's where Z38xx gets it from.

Ed

Yes, once I moved the antenna outside, it started behaving normally. The satellites it is having issues with are those at low elevation, particularly those to the south of me. This isn't surprising given the position of the antenna.  I need to figure out a good solution to run the coax from outside into the room here, and then I can mount the antenna in a more permanent location. Unfortunately, I'll have to bring it inside tomorrow.

I'll post some of the Z38XX graphs after it's had a bit more time to run.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on July 26, 2015, 03:55:38 am
Do you know what the receiver is inside the gps box?.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 04:28:33 am
Do you know what the receiver is inside the gps box?.

If you send this command via the RS422 Diagnostics port:

:DIAG:IDEN:GPS?

It reports this:

"COPYRIGHT 1991-1997 MOTOROLA INC.","SFTW P/N #     98-P36848P ","SOFTWARE VER # 2          ","SOFTWARE REV # 2          ","SOFTWARE DATE  APR 24 1998","MODEL #    R5122U1152     ","HWDR P/N # 5              ","SERIAL #   R05582         ","MANUFACTUR DATE 9D12      ","                          "
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 26, 2015, 08:24:48 am
Do you know what the receiver is inside the gps box?.
If you send this command via the RS422 Diagnostics port:
:DIAG:IDEN:GPS?
It reports this:
"COPYRIGHT 1991-1997 MOTOROLA INC.","SFTW P/N #     98-P36848P ","SOFTWARE VER # 2          ","SOFTWARE REV # 2          ","SOFTWARE DATE  APR 24 1998","MODEL #    R5122U1152     ","HWDR P/N # 5              ","SERIAL #   R05582         ","MANUFACTUR DATE 9D12      ","                          "

Motorola UT+ Oncore GPS Timing Receiver p/n R5122U1152
According to http://do-nyc.bodosom.net/ (http://do-nyc.bodosom.net/)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 12:37:42 pm
Well, I'm a happy camper as I was just able to calibrate my 53131A with this reference.

I tried to calibrate it last night, but it kept failing calibration. I hooked a scope up to the GPSDO 10MHz output of the Z3812A and the output of the internal 10MHz OCXO in the 53131A, and then ran a calibration cycle. After doing this, it was really clear that the 53131A was not able to adjust the EFC on the OCXO (the frequency never changed). I removed the OCXO and noticed there was a header on the board that was supposed to have a jumper on it. The jumper selects between adjustment of the EFC with a 10-turn pot or with a D/A chip (i.e. auto-calibration by the 53131A micro). You can find both versions of this OCXO on eBay - one with the 10-turn pot and one with the extra circuitry to allow auto-calibration. I guess the seller forgot to install the jumper, or perhaps it fell off in shipping. In any event, I popped a jumper on there, and it auto-calibrated within 0.001 Hz first try.

Here's a screen capture of the data displayed by the Z38XX program. There's a big gap in the charts because my computer went to sleep last night. The stability looks similar to that shown in Ed's chart - it bounces back and forth between +/-40ns. HUD was very high, but after running with a GPS lock for some time, it finally dropped to 8.7us.

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 26, 2015, 03:34:11 pm
Here's a screen capture of the data displayed by the Z38XX program. There's a big gap in the charts because my computer went to sleep last night. The stability looks similar to that shown in Ed's chart - it bounces back and forth between +/-40ns. HUD was very high, but after running with a GPS lock for some time, it finally dropped to 8.7us.

I'm glad you were able to calibrate your counter.  If you decide to leave your GPSDO online permanently, you could consider using it as the external reference for your counter.  The short-term jitter might be a problem.  I haven't tried that.

The EFC on mine was wandering up and down, which caused the HUP to do the same.  Your EFC looks much nicer.  Your HUP will likely keep dropping.  As that happens, you should see a decrease in the peak-to-peak excursions on the time interval graph.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 04:42:28 pm
Here's a screen capture of the data displayed by the Z38XX program. There's a big gap in the charts because my computer went to sleep last night. The stability looks similar to that shown in Ed's chart - it bounces back and forth between +/-40ns. HUD was very high, but after running with a GPS lock for some time, it finally dropped to 8.7us.

I'm glad you were able to calibrate your counter.  If you decide to leave your GPSDO online permanently, you could consider using it as the external reference for your counter.  The short-term jitter might be a problem.  I haven't tried that.

The EFC on mine was wandering up and down, which caused the HUP to do the same.  Your EFC looks much nicer.  Your HUP will likely keep dropping.  As that happens, you should see a decrease in the peak-to-peak excursions on the time interval graph.

Ed

I really do want to leave it on, although until I get the cable/antenna situation sorted out, I will have to at least bring the antenna back inside. I suppose there's value in leaving it on even then as it will help the OCXOs to age.

The HUD on mine has dropped to 3.5us now, btw.

Ed - thanks a lot for all your help. It is much appreciated.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 26, 2015, 04:51:05 pm
I found out why my RFTG-0 unit was AFU, turns out I must have damaged a resistor causing the EFC voltage to wonder from one extreme to another. Replaced the damaged part and it seems to be working again  :phew:
From a cold start it takes less than 20 minutes for the NO GPS to go off using a decent outdoor antenna.
Stability seems ok for my needs. After running overnight  and sitting directly under a ceiling fan and the AC cycling the short term frequency deviates less than .0004Hz  according to my 53131A.
Still getting gibberish from com port. Tried several different Prolific RS232 to USB adapters on 2 different PC's, Win 7 and XP. Must be something real obvious that I am missing and just dont see it ?

Here's the pinout of J6 if anyone is interested:
J6 goes to U37, U38, U39 (75176 Differential Bus Transceiver)

J6.1 --- U38.6
J6.2 --- NC
J6.3 --- GND
J6.4 --- U39.6
J6.5 --- U37.6
J6.6 --- U38.7
J6.7 --- GND
J6.8 --- U39.7
J6.9 --- U37.7
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 06:00:08 pm
I found out why my RFTG-0 unit was AFU, turns out I must have damaged a resistor causing the EFC voltage to wonder from one extreme to another. Replaced the damaged part and it seems to be working again  :phew:
From a cold start it takes less than 20 minutes for the NO GPS to go off using a decent outdoor antenna.
Stability seems ok for my needs. After running overnight  and sitting directly under a ceiling fan and the AC cycling the short term frequency deviates less than .0004Hz  according to my 53131A.
Still getting gibberish from com port. Tried several different Prolific RS232 to USB adapters on 2 different PC's, Win 7 and XP. Must be something real obvious that I am missing and just dont see it ?

Here's the pinout of J6 if anyone is interested:
J6 goes to U37, U38, U39 (75176 Differential Bus Transceiver)

J6.1 --- U38.6
J6.2 --- NC
J6.3 --- GND
J6.4 --- U39.6
J6.5 --- U37.6
J6.6 --- U38.7
J6.7 --- GND
J6.8 --- U39.7
J6.9 --- U37.7

Hi N8AUM -

How did you damage that resistor? I am curious if it was via some external connector, and if so what the cautionary note on that is.

Here is the RS-422 set-up that I have. Note that I am connected to J8, not J6. J8 is the port where you can send commands and monitor status. J6 also has an RS-422 interface, which outputs a time string, but I have not seen any info on what commands you
can send there. It may be a read-only thing.

I am using a Gearmo USB to RS-485/RS-422 Converter, model # US-485422.
Link to product on Gearmo.com: http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/ (http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/)
Link to product on Amazon: http://www.amazon.com/gp/product/B005CPLOVW (http://www.amazon.com/gp/product/B005CPLOVW)

The Gearmo uses an FTDI chip, and they have a download link to the FTDI drivers on their web site. You can also just grab the FTDI drivers from their web site (ftdichip.com). I believe the FTDI chip is RS232RL. It's also possible that the drivers can be installed via Windows Update; I couldn't tell if that was the case because I already had the driver installed on my machine.

The Gearmo product comes with a little terminal board connected to a DB9-male connector. The terminal strip connections are labelled and match the names below (T/R+, RXD+, etc.). Note that the Gearmo documentation, and labels on the terminal strip, refer to "TXD" as "T/R".

Gearmo         RTFG-u/REF0/1 J8
--------       ----------------
1 (T/R+)  -->  4 (RX+)
2 (T/R-)  -->  8 (RX-)
3 (RXD+)  <--  5 (TX+)
4 (RXD-)  <--  9 (TX-)
5 (GND)   ---  7 (GND)


I am using the little DB9-to-terminal strip adapter that comes with the Gearmo to connect up to another terminal strip to DB9 adapter and swap the wiring. I can't recommend the terminals trip adapter that I bought for that, however, as I ended up having to dremel off some bits to get it to fit. I'll replace all this with a custom cable when the parts arrive next week.

The unit came up set for 9600/N/8/1 when it first booted. There appears to be a command to change the baud rate, but I haven't tried that.

Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 26, 2015, 07:20:11 pm
Thanks for the info Moto !
It was my fault that caused damage. I removed the board to look around for a good point to tap off 10Mhz sine output. Anyways, when I was putting the board back into the case I must have hit the resistor on one of the chassis mounting lugs that the board is mounted to.
Off I go to put a little more altitude on one of the GPS antennas.

tnx again 73
Vidas
 
Title: Re: Economical option for precision frequency reference?
Post by: johnny_canuck on July 26, 2015, 07:26:15 pm
FWIW. I have a Thunderbolt GPSDO and a $5 car-top mag-mount amplified antenna from e-bay that looks like a hockey-puck. It's mounted at 25 feet to clear the peak of my roof and fed with about 50 feet of cable TV coax. One hour after a cold start I have acquired seven of eight possible satellites and the 10 MHz output is within +/- .05 ppb according to the T-bolt monitor programme.

Ken
Toronto, Canada
Title: Re: Economical option for precision frequency reference?
Post by: wiss on July 26, 2015, 07:59:51 pm
I ordered a ~20€ dcf77 receiver of ebay today, I just have to see if it is any usefull as frequency reference.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 08:28:40 pm
FWIW. I have a Thunderbolt GPSDO and a $5 car-top mag-mount amplified antenna from e-bay that looks like a hockey-puck. It's mounted at 25 feet to clear the peak of my roof and fed with about 50 feet of cable TV coax. One hour after a cold start I have acquired seven of eight possible satellites and the 10 MHz output is within +/- .05 ppb according to the T-bolt monitor programme.

Ken
Toronto, Canada

I am not all that familiar with the Thunderbolt, but I suspect it uses a newer and more sensitive GPS chipset. Unfortunately, the price on the Thunderbolts has creaped up over the years. It was about 3x more expensive than this Lucent model, IIRC.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 26, 2015, 09:45:43 pm
I have a Thunderbird also but its an older version and twice as wide. Its front end isnt too bad, able to pick up 4 birds with an el-cheapo Chinese mag mount inside the house.
Those new GPSDO on fleabay from China are using much newer (AND BETTER) front ends. All 3 of mine will lock on to 4 birds with just a 2" piece of wire stuck into the antenna jack.

On those $5 GPS antennas I found that the round ones have at least 2 units stronger received signal than the squarish types.

Just stuck one of the round ones on a 20ft. pole wich is above my roof so now I will have a CLEAR view of all the birds.
 
Vidas
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 09:49:45 pm
I have a Thunderbird also but its an older version and twice as wide. Its front end isnt too bad, able to pick up 4 birds with an el-cheapo Chinese mag mount inside the house.
Those new GPSDO on fleabay from China are using much newer (AND BETTER) front ends. All 3 of mine will lock on to 4 birds with just a 2" piece of wire stuck into the antenna jack.

On those $5 GPS antennas I found that the round ones have at least 2 units stronger received signal than the squarish types.

Just stuck one of the round ones on a 20ft. pole wich is above my roof so now I will have a CLEAR view of all the birds.
 
Vidas

Can you post a link to the newer/better GPSDO you are speaking of? THere are a lot of GPSDO on eBay.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 26, 2015, 10:01:12 pm
I have a Thunderbird also but its an older version and twice as wide. Its front end isnt too bad, able to pick up 4 birds with an el-cheapo Chinese mag mount inside the house.
Those new GPSDO on fleabay from China are using much newer (AND BETTER) front ends. All 3 of mine will lock on to 4 birds with just a 2" piece of wire stuck into the antenna jack.

On those $5 GPS antennas I found that the round ones have at least 2 units stronger received signal than the squarish types.

Just stuck one of the round ones on a 20ft. pole wich is above my roof so now I will have a CLEAR view of all the birds.
 
Vidas

Can you post a link to the newer/better GPSDO you are speaking of? THere are a lot of GPSDO on eBay.

After I purchased 4 of these he jacked his price up LOL
I really like these units, nice and small AND brand new except for the salvaged OCXO they are using.
They have 2 flavors, sine or square wave output so do a search on them.
One thing I read about these tho is that there is a slight bug in its firmware and they run just a touch on the slow side but its so minute that I cant measure it nor will it make any difference for me. I think its somere in the beginning of this thread ?

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590)

Wiss, Let us know how your new toy works when you get it

 
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 26, 2015, 10:22:05 pm
After I purchased 4 of these he jacked his price up LOL
I really like these units, nice and small AND brand new except for the salvaged OCXO they are using.
They have 2 flavors, sine or square wave output so do a search on them.
One thing I read about these tho is that there is a slight bug in its firmware and they run just a touch on the slow side but its so minute that I cant measure it nor will it make any difference for me. I think its somere in the beginning of this thread ?

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590)

Wiss, Let us know how your new toy works when you get it

Are you sure these are the ones you bought?  I've just noticed that there are now three different GPSDOs on ebay that all have this same aluminum+PCB case.  The one you posted actually uses an Oscilloquartz 'Star 4' board.  I found a datasheet on that, but no user manual.  The second is the home-made one that appears to be running slightly slow.  The third is a Trimble unit.  I bought the bare Trimble unit from somewhere else and just powered it up yesterday.  I can't find any data on it, but it uses a command set that is somewhat similar to the Z38xx series.  It only took about 10 minutes from a cold start to figure out where it was and lock the oscillator!  I didn't even have time to get the PC connected!

Ed
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 26, 2015, 10:32:35 pm
Your right, these are something new, sorry about that. The ones I got are the ones with the MORION OCXO: http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/181793953652?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3Dc0a0dd3ba68d468a8bd57e5c5a38479e%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D181800366117 (http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/181793953652?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3Dc0a0dd3ba68d468a8bd57e5c5a38479e%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D181800366117)

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 26, 2015, 10:55:26 pm
Your right, these are something new, sorry about that. The ones I got are the ones with the MORION OCXO: http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/181793953652?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3Dc0a0dd3ba68d468a8bd57e5c5a38479e%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D181800366117 (http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/181793953652?_trksid=p2047675.c100005.m1851&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20131003132420%26meid%3Dc0a0dd3ba68d468a8bd57e5c5a38479e%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D181800366117)

Okay, thanks.  Unfortunately, those are the ones that are running a bit slow.  I also don't understand that Allan Deviation graph.  The disciplining doesn't seem to be working right.  But unless you're a Time-Nut, the performance will be pretty good.   :)

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 26, 2015, 11:52:09 pm
After I purchased 4 of these he jacked his price up LOL
I really like these units, nice and small AND brand new except for the salvaged OCXO they are using.
They have 2 flavors, sine or square wave output so do a search on them.
One thing I read about these tho is that there is a slight bug in its firmware and they run just a touch on the slow side but its so minute that I cant measure it nor will it make any difference for me. I think its somere in the beginning of this thread ?

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590)

Wiss, Let us know how your new toy works when you get it

Are you sure these are the ones you bought?  I've just noticed that there are now three different GPSDOs on ebay that all have this same aluminum+PCB case.  The one you posted actually uses an Oscilloquartz 'Star 4' board.  I found a datasheet on that, but no user manual.  The second is the home-made one that appears to be running slightly slow.  The third is a Trimble unit.  I bought the bare Trimble unit from somewhere else and just powered it up yesterday.  I can't find any data on it, but it uses a command set that is somewhat similar to the Z38xx series.  It only took about 10 minutes from a cold start to figure out where it was and lock the oscillator!  I didn't even have time to get the PC connected!

Ed

Is this the newer Trimble unit to which you are referring?

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 27, 2015, 12:25:04 am
Thanks for the info Moto !
It was my fault that caused damage. I removed the board to look around for a good point to tap off 10Mhz sine output. Anyways, when I was putting the board back into the case I must have hit the resistor on one of the chassis mounting lugs that the board is mounted to.
Off I go to put a little more altitude on one of the GPS antennas.

tnx again 73
Vidas

You are welcome. I just moved my RS422 connection over to J6. And it's outputting strings like this:

:110100001842E03C7DA401AA
:110100001842E03C7EA401AB
:110100001842E03C7FA401AC

I am not familiar with this format, but maybe someone else here is?

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 27, 2015, 01:42:03 am
After I purchased 4 of these he jacked his price up LOL
I really like these units, nice and small AND brand new except for the salvaged OCXO they are using.
They have 2 flavors, sine or square wave output so do a search on them.
One thing I read about these tho is that there is a slight bug in its firmware and they run just a touch on the slow side but its so minute that I cant measure it nor will it make any difference for me. I think its somere in the beginning of this thread ?

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224?hash=item1a02d36590)

Wiss, Let us know how your new toy works when you get it

Are you sure these are the ones you bought?  I've just noticed that there are now three different GPSDOs on ebay that all have this same aluminum+PCB case.  The one you posted actually uses an Oscilloquartz 'Star 4' board.  I found a datasheet on that, but no user manual.  The second is the home-made one that appears to be running slightly slow.  The third is a Trimble unit.  I bought the bare Trimble unit from somewhere else and just powered it up yesterday.  I can't find any data on it, but it uses a command set that is somewhat similar to the Z38xx series.  It only took about 10 minutes from a cold start to figure out where it was and lock the oscillator!  I didn't even have time to get the PC connected!

Ed

Is this the newer Trimble unit to which you are referring?

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9)

That's the one.  It's also available as a bare board here:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)

I bought the bare board somewhere else.  Here's what syst:stat reports:

UCCM >syst:stat?

-------------------------------------------------------------------------------
57964-05     serial number  84466200     firmware ver  1.0.0.2-01 W-CDMA  mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]
XX Ref 8KHz 1: [LOS]                          TFOM     2            FFOM      0
XX Ref 8KHz 2: [LOS]                          UCCM A Status[ALARM]
XX Ref 8KHz 3: [LOS]
>> GPS: [phase:+9.8E-09]
ACQUISITION ...................................................[GPS 1PPS Valid]
Tracking: 7 ____   Not Tracking: 0 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      23:35:21     26 Jul 2015
 25  52 253   49
 20  15 198   43                              ANT DLY  0 ns
 12  39 196   46                              Position ________________________
  2  63  68   45                              MODE     Hold
 29  43 297   42
  5  54 153   47                              LAT      N  50:28:somewhere
  6  22  68   35                              LON      W 104:37:somewhere
                                              HGT              +560.74 m (MSL)




ELEV MASK 15 deg
-------------------------------------------------------------------------------

Command complete
UCCM >


Similar to the Z38xx units, but not the same. 

It looks like it has a 12-channel receiver - there are 5 blank lines under the list of tracked satellites.  Like most of the Trimble GPSDOs, there's no info available on the OCXO.  The biggest drawback is that there's no info on the commands that it does accept and no software like Z38xx to monitor it.  Performance is okay.  It's been running for less than a day, so Allan Deviation is similar to the RFTG, but it looks like the disciplining is working better than the RFTG.  Or maybe, the OCXO is just better behaved.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on July 27, 2015, 02:06:38 am
I've found one of those old Rockwell "Jupiter" GPS boards in a back drawer. Apparently it's good because it has a 10kHz GPS derived frequency standard that can be used in a PLL with a TXCO to give a GPS disciplined 10 MHz... http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm (http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm)

Unfortunately I am not getting anything out of it on the RS232 pins (crappy non standard header doesn't help!). I think I have to set some pull ups and grounds correctly.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 27, 2015, 02:09:49 am

Is this the newer Trimble unit to which you are referring?
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9)

That's the one.  It's also available as a bare board here:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)

How have you (or have  you) housed the bare board? I would worry about heat disappation if it is housed in that aluminum box shown on the eBay listing I posted. In the photos there, it looks like there is a second PCB underneath the Trimble PCB. I wonder what that is.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 27, 2015, 02:28:17 am

Is this the newer Trimble unit to which you are referring?
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power-/181810679481?hash=item2a54c2ceb9)

That's the one.  It's also available as a bare board here:

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)

How have you (or have  you) housed the bare board? I would worry about heat disappation if it is housed in that aluminum box shown on the eBay listing I posted. In the photos there, it looks like there is a second PCB underneath the Trimble PCB. I wonder what that is.

It's just sitting on my bench.  The OCXO does get quite toasty, but the rest of it is fine.  It runs off 5V and draws 2 amps at startup and 1 amp after warmup.  There's no easy way to tell how much of that is going to the oven.  Heat dissipation in a closed case is something to think about, but that's a good size box so it's probably okay.  It actually helps an OCXO to house it in a way that keeps drafts away from it.

The lower board in the picture is the interface board.  The builder took the existing Trimble board and mounted it on an interface board that he created to handle power and connectors.

Ed

P.S.  Hey, this makes 104 replies in this thread and over 3700 views!  I guess somebody's interested in our little chat!  :)
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 27, 2015, 02:43:31 am
I've found one of those old Rockwell "Jupiter" GPS boards in a back drawer. Apparently it's good because it has a 10kHz GPS derived frequency standard that can be used in a PLL with a TXCO to give a GPS disciplined 10 MHz... http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm (http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm)

Unfortunately I am not getting anything out of it on the RS232 pins (crappy non standard header doesn't help!). I think I have to set some pull ups and grounds correctly.

The 10 KHz gives you the ability to use analog PLL techniques.  That's what Miller did.  If you only have 1 PPS to work with, you pretty much need to go to digital PLLs and microprocessors.

Non-standard header?  The 'classic' board is the TU30 which has a 2x10 header on 0.1" centers.  It doesn't get more standard than that.  You must have a different model.  Jupiter was a product line so there are multiple models.  I think some of them have headers with 2 mm spacing.  Consider yourself lucky.  I've got a board that has a header on 0.05" centers.

Are you using something like a MAX232 to convert the signals from TTL to RS-232?  If not, you might need to invert the signals.  I've heard of people feeding TTL signals directly into a COM port, but I've never done it myself so I don't know the details.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 27, 2015, 03:35:24 am
Here is a summary of the info I've collected on the Lucent KS-24361 so far. Hopefully this saves someone from having to subject themselves to TimeNuts mailing list archives. By the way - see below for details on that continous output from connector J6 that I pasted earlier in the thread.


Useful Links
EEVBlog Thread (here):
  https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/ (https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/)

Time Nuts thread with pinouts and other details:
  http://permalink.gmane.org/gmane.comp.time.nuts/40898 (http://permalink.gmane.org/gmane.comp.time.nuts/40898)

Original Time Nuts thread:
  https://www.febo.com/pipermail/time-nuts/2014-October/087274.html (https://www.febo.com/pipermail/time-nuts/2014-October/087274.html)


J6 (RS422/1PPS) Pinout

1 - PPS+
3 - GND
4 - RX+
5 - TX+
6 - PPS-
7 - GND
8 - RX-
9 - TX-

All others not connected


J8 (Diagnostic) Pinout

3 - GND
4 - RX+
5 - TX+
7 - GND
8 - RX-
9 - TX-

All others not connected


Info on interfacing to PC using the Gearmo USB to RS-422 converter

Gearmo USB to RS-485/RS-422 Converter, model # US-485422.
Link to product on Gearmo.com: http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/ (http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/)
Link to product on Amazon: http://www.amazon.com/gp/product/B005CPLOVW (http://www.amazon.com/gp/product/B005CPLOVW)

The Gearmo uses an FTDI chip, and they have a download link to the FTDI drivers on their web site. You can also just grab the FTDI drivers from their web site (ftdichip.com). I believe the FTDI chip is RS232RL. It's also possible that the drivers can be installed via Windows Update

The Gearmo product comes with a little terminal board connected to a DB9-male connector. The terminal strip connections are labelled and match the names below (T/R+, RXD+, etc.). Note that the Gearmo documentation, and labels on the terminal strip, refer to "TXD" as "T/R".

Gearmo         RTFG-u/REF0/1 J6 & J8
--------       ----------------
1 (T/R+)  -->  4 (RX+)
2 (T/R-)  -->  8 (RX-)
3 (RXD+)  <--  5 (TX+)
4 (RXD-)  <--  9 (TX-)
5 (GND)   ---  7 (GND)


J6 Continuous Output

J6 starts up in a mode where it continuously emits time strings (see format below). You can switch it
into interactive mode by sending this command:
  :ptim:tcod:cont 0
To switch back to continuous time mode, send this command:
  :ptim:tcod:cont 1

Here is a sample output of J6 from my KS-24361 (REF 1):
  :110100001842E03C7FA401AC

This string is a ':' character followed by 24 hex digits
character
(hex ascii)  use         values
-----------  -------     ---------------------------------------------
0            ':'         Line always starts with ':'
1            talker      0 = ref 0, 1 = ref 1
2            status      0 = active, 1 = inactive
3            (unused)    0
4            mode        0 = warmup, 1 = gps, 2 = holdover, 3 = fault
5 to 8       (unused)    0000
9,10         time        hours in this mode
11 to 18     GPS time    seconds since GPS start in 1980
19 to 22     Firmware    Rom version
23,24        checksum   


Use this site to convert GPS time (convert the number from hex to decimal first):
  http://www.andrews.edu/~tzs/timeconv/timeconvert.php? (http://www.andrews.edu/~tzs/timeconv/timeconvert.php?)

The sample output above translates to:

  Talker=Ref 1
  Status=Inactive
  --
  Mode=GPS
  Hours in mode=0x18 (24)
  GPS time = 0x42E03C7F (1121991807) -> 2015-07-27 00:23:10 UTC
  ROM version = 0xA401
  Checksum = 0xAC (Sum each byte (two hex digits) and take the low order byte of the result).


Some useful commands:
:SYST:STAT?
  (Dumps useful status info)
:GPS:POS:SURV:PROG?
  (Shows survey progress)
:GPS:INIT:DATE YYYY,MM,DD
:GPS:INIT:TIME HH,MM,SS
  (Date and time in UTC)
:GPS:INIT:POS N|S,DD,MM,SS.SSS,W|E,DDD,MM,SS.SSS,AAA
  (AAA is altitude above MSL in meters)
:DIAG:LOG:READ:ALL?
  (Dumps log)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 27, 2015, 03:37:09 am
P.S.  Hey, this makes 104 replies in this thread and over 3700 views!  I guess somebody's interested in our little chat!  :)

Yes indeed. I can't speak for others, but I've had great fun playing around with this Lucent unit this weekend. Thanks much for all your help!
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 27, 2015, 03:50:28 am
P.S.  Hey, this makes 104 replies in this thread and over 3700 views!  I guess somebody's interested in our little chat!  :)

Yes indeed. I can't speak for others, but I've had great fun playing around with this Lucent unit this weekend. Thanks much for all your help!

You're very welcome!  I enjoy reverse-engineering things and getting them running again.  Best puzzle-solving fun there is!  But beware..... These things can become addictive.  Don't ask how I know! :palm:

Ed
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on July 27, 2015, 04:17:48 am
The 10 KHz gives you the ability to use analog PLL techniques.  That's what Miller did.  If you only have 1 PPS to work with, you pretty much need to go to digital PLLs and microprocessors.

Non-standard header?  The 'classic' board is the TU30 which has a 2x10 header on 0.1" centers.  It doesn't get more standard than that.  You must have a different model.  Jupiter was a product line so there are multiple models.  I think some of them have headers with 2 mm spacing.  Consider yourself lucky.  I've got a board that has a header on 0.05" centers.
Indeed, mine are 0.07" - and it is the TU30 board, JUP8 V180 firmware, all the ICs are dated late 1999.
(http://i.imgur.com/7v7dK0f.jpg)
(http://i.imgur.com/jnypzah.jpg)
Quote
Are you using something like a MAX232 to convert the signals from TTL to RS-232?  If not, you might need to invert the signals.  I've heard of people feeding TTL signals directly into a COM port, but I've never done it myself so I don't know the details.
Yeah, I've used a CP2102 USB/UART. I've also had my 'scope on the RX and TX lines and there is nothing there. :(

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 27, 2015, 06:01:53 am
The 10 KHz gives you the ability to use analog PLL techniques.  That's what Miller did.  If you only have 1 PPS to work with, you pretty much need to go to digital PLLs and microprocessors.

Non-standard header?  The 'classic' board is the TU30 which has a 2x10 header on 0.1" centers.  It doesn't get more standard than that.  You must have a different model.  Jupiter was a product line so there are multiple models.  I think some of them have headers with 2 mm spacing.  Consider yourself lucky.  I've got a board that has a header on 0.05" centers.
Indeed, mine are 0.07" - and it is the TU30 board, JUP8 V180 firmware, all the ICs are dated late 1999.

Quote
Are you using something like a MAX232 to convert the signals from TTL to RS-232?  If not, you might need to invert the signals.  I've heard of people feeding TTL signals directly into a COM port, but I've never done it myself so I don't know the details.
Yeah, I've used a CP2102 USB/UART. I've also had my 'scope on the RX and TX lines and there is nothing there. :(

You're right!  I don't know where I came up with 0.1", the header is 2 mm.  Sorry for the mistake.  One of mine is identical to yours.  It's the one that mysteriously died on me one day for no good reason.   :(  Maybe there's a pattern here.......

For anyone who's reading this, it looks like 'data inversion' isn't an issue here.  Since each transceiver inverts the data and Macbeth has removed both transceivers, the data polarity should be correct.

I'm not familiar with the CP2102.  I see that it's powered from 3.3 volts.  The Jupiter is powered from 5V and the minimum high level input voltage is 0.7 x PWRIN.  The CP2102 might not be able to drive the Jupiter.

Other than that, all I can suggest is to check your jumpers against the data sheet.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 27, 2015, 06:15:40 pm
Here is a summary of the info I've collected on the Lucent KS-24361 so far. Hopefully this saves someone from having to subject themselves to TimeNuts mailing list archives. By the way - see below for details on that continous output from connector J6 that I pasted earlier in the thread.


Useful Links
EEVBlog Thread (here):
  https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/ (https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/)

Time Nuts thread with pinouts and other details:
  http://permalink.gmane.org/gmane.comp.time.nuts/40898 (http://permalink.gmane.org/gmane.comp.time.nuts/40898)

Original Time Nuts thread:
  https://www.febo.com/pipermail/time-nuts/2014-October/087274.html (https://www.febo.com/pipermail/time-nuts/2014-October/087274.html)


J6 (RS422/1PPS) Pinout

1 - PPS+
3 - GND
4 - RX+
5 - TX+
6 - PPS-
7 - GND
8 - RX-
9 - TX-

All others not connected


J8 (Diagnostic) Pinout

3 - GND
4 - RX+
5 - TX+
7 - GND
8 - RX-
9 - TX-

All others not connected


Info on interfacing to PC using the Gearmo USB to RS-422 converter

Gearmo USB to RS-485/RS-422 Converter, model # US-485422.
Link to product on Gearmo.com: http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/ (http://www.gearmo.com/shop/usb-to-rs485-rs422-converter-with-ftdi-chip/)
Link to product on Amazon: http://www.amazon.com/gp/product/B005CPLOVW (http://www.amazon.com/gp/product/B005CPLOVW)

The Gearmo uses an FTDI chip, and they have a download link to the FTDI drivers on their web site. You can also just grab the FTDI drivers from their web site (ftdichip.com). I believe the FTDI chip is RS232RL. It's also possible that the drivers can be installed via Windows Update

The Gearmo product comes with a little terminal board connected to a DB9-male connector. The terminal strip connections are labelled and match the names below (T/R+, RXD+, etc.). Note that the Gearmo documentation, and labels on the terminal strip, refer to "TXD" as "T/R".

Gearmo         RTFG-u/REF0/1 J6 & J8
--------       ----------------
1 (T/R+)  -->  4 (RX+)
2 (T/R-)  -->  8 (RX-)
3 (RXD+)  <--  5 (TX+)
4 (RXD-)  <--  9 (TX-)
5 (GND)   ---  7 (GND)


J6 Continuous Output

J6 starts up in a mode where it continuously emits time strings (see format below). You can switch it
into interactive mode by sending this command:
  :ptim:tcod:cont 0
To switch back to continuous time mode, send this command:
  :ptim:tcod:cont 1

Here is a sample output of J6 from my KS-24361 (REF 1):
  :110100001842E03C7FA401AC

This string is a ':' character followed by 24 hex digits
character
(hex ascii)  use         values
-----------  -------     ---------------------------------------------
0            ':'         Line always starts with ':'
1            talker      0 = ref 0, 1 = ref 1
2            status      0 = active, 1 = inactive
3            (unused)    0
4            mode        0 = warmup, 1 = gps, 2 = holdover, 3 = fault
5 to 8       (unused)    0000
9,10         time        hours in this mode
11 to 18     GPS time    seconds since GPS start in 1980
19 to 22     Firmware    Rom version
23,24        checksum   


Use this site to convert GPS time (convert the number from hex to decimal first):
  http://www.andrews.edu/~tzs/timeconv/timeconvert.php? (http://www.andrews.edu/~tzs/timeconv/timeconvert.php?)

The sample output above translates to:

  Talker=Ref 1
  Status=Inactive
  --
  Mode=GPS
  Hours in mode=0x18 (24)
  GPS time = 0x42E03C7F (1121991807) -> 2015-07-27 00:23:10 UTC
  ROM version = 0xA401
  Checksum = 0xAC (Sum each byte (two hex digits) and take the low order byte of the result).


Some useful commands:
:SYST:STAT?
  (Dumps useful status info)
:GPS:POS:SURV:PROG?
  (Shows survey progress)
:GPS:INIT:DATE YYYY,MM,DD
:GPS:INIT:TIME HH,MM,SS
  (Date and time in UTC)
:GPS:INIT:POS N|S,DD,MM,SS.SSS,W|E,DDD,MM,SS.SSS,AAA
  (AAA is altitude above MSL in meters)
:DIAG:LOG:READ:ALL?
  (Dumps log)


This is really great info!

Plan to get the GEARMO!!!

Thankyou!
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 28, 2015, 03:13:45 am
I am looking at the EFC and PPS graph in Z38XX. I think the PID loop that is controlling the EFC is not tuned very well. It looks massively underdamped. It's ashame we don't have access to the firmware, because that is so fixable.
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 28, 2015, 03:44:28 am
There's some other information that may be relevant to the Lucent RFTG units at these links:
http://www.prc68.com/I/KS-24361.html (http://www.prc68.com/I/KS-24361.html)
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing (http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing)

Does the GPS input of the unit happen to supply a DC bias voltage out for powering an external active antenna or must the antenna be powered externally if needed?

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 28, 2015, 04:10:42 am
There's some other information that may be relevant to the Lucent RFTG units at these links:
http://www.prc68.com/I/KS-24361.html (http://www.prc68.com/I/KS-24361.html)
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing (http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing)

Does the GPS input of the unit happen to supply a DC bias voltage out for powering an external active antenna or must the antenna be powered externally if needed?

Yes, it provides 5V.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 28, 2015, 04:28:00 am
There's some other information that may be relevant to the Lucent RFTG units at these links:
http://www.prc68.com/I/KS-24361.html (http://www.prc68.com/I/KS-24361.html)
http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing (http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=02_GPS_Timing)

Does the GPS input of the unit happen to supply a DC bias voltage out for powering an external active antenna or must the antenna be powered externally if needed?

It provides 5 Volts @ 130ma
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 28, 2015, 04:39:54 am
Thanks for the antenna power and all the other information here.
Title: Re: Economical option for precision frequency reference?
Post by: VE7FM on July 28, 2015, 05:02:01 am
I have been considering buying a Nortel Trimble NTBW50AA from ebay. It has a 10 MHz out and a 9.8304 MHz out. I have two pieces of test gear I'd like to connect to it. Both accept 10 MHz in but one also accepts 19.6608 MHz. I was thinking I could connect the 10 MHz out to one piece of gear and possibly use the 9.8304 MHz out for the second with a frequency doubler. Does anyone have any thoughts on using a doubler and if so any recommended schematics?
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 28, 2015, 06:40:35 am
I am looking at the EFC and PPS graph in Z38XX. I think the PID loop that is controlling the EFC is not tuned very well. It looks massively underdamped. It's ashame we don't have access to the firmware, because that is so fixable.

Funny you should mention that!  ;D  Take a look at this message thread:

https://www.febo.com/pipermail/time-nuts/2013-May/076625.html (https://www.febo.com/pipermail/time-nuts/2013-May/076625.html)

It turns out there's a pForth interpreter hiding inside these boxes.  I didn't check this on the Lucent box, but it looks like this guy did:

http://do-nyc.bodosom.net/ (http://do-nyc.bodosom.net/)

I don't know if there's enough info or control to allow you to tinker with the loop parameters.  I don't know if anyone has experimented with it.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 28, 2015, 02:19:29 pm
Apparently the 10 MHz output on REF-0 is relatively unclean. However, at least one person has built a nice circuit to double, filter, and amplify the 5 MHz into a nice clean set of 4 10 MHz, +10dBm signals:

http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf (http://www.hoffmann-hochfrequenz.de/downloads/DoubDist.pdf)

It would be great to get a PCB made for this. Unfortunately, I am not a PCB guy; the last  PCB I did was in the last century :P
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 28, 2015, 04:40:16 pm
I understand that the 10MHz 'test point' output is said to be jittery and perhaps due to an underdamped loop.
But is it confirmed that that remains to be the case even after the unit has stabilized with a good signal lock for several days or weeks so that everything 'settles down'?

How clean is the 'primary' 15MHz output, qualitatively or quantitatively?

As for a PCB for the 5MHz processing doubler and distribution amp, I could make some gerber files that would be compatible with OSHPark, Seeedstudio, elecrow, dirtypcbs, et. al. publically available in the near future if there is continued interest and I can get the CAD data on the particular parts involved in the publication.

Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on July 28, 2015, 07:13:04 pm
If ths 15Mhz is created in the same way as the old one, you should be able yo bypass the the 15mhz filter as pass the 10mhz to the output amplifier.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 29, 2015, 12:00:07 am
Received my GearMo today and it works great ! Turns out my old 422 converter took a dump. Also ordered a cheaper converter that worked 1 time, yup, it has the counterfeit FTDI chip.

So far the receiver sees 9 birds and tracks 8 of them as compared to 12 out of 15 with something that was made in this past century and with an indoor antenna lol 

oh, the counterfeit FTDI works fine with the drivers that came with the unit on my Win XP machine but not Win 7. Guess you get what you pay for !
 
http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 (http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00)

 
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 29, 2015, 12:12:52 am
If ths 15Mhz is created in the same way as the old one, you should be able yo bypass the the 15mhz filter as pass the 10mhz to the output amplifier.

I found a 10 Mhz sine signal that appears to be coming from a simple freq doubler which goes to a Schmitt trigger to get squared off that I think eventually comes out the 10 Mhz TP (J1). Think I will run that into some sort of driver and make that my 10 Mhz reference source rather than trying to filter the square wave.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 12:40:01 am
I understand that the 10MHz 'test point' output is said to be jittery and perhaps due to an underdamped loop.
But is it confirmed that that remains to be the case even after the unit has stabilized with a good signal lock for several days or weeks so that everything 'settles down'?

I am inferring from the Time-Nuts emails that the problem is more about the way the 10 MHz signal is derived from the 5MHz reference, and not the jitter caused by the EFC corrections. Since the EFC corrections are to the 5 MHz DOCXO, which then drives all the other frequencies, I expect the impact of the EFC corrections will be in all the signals.

I simply am not qualified to comment further on it. Looking at the signal on my scope, I do see a fair amount of 5 Mhz mixed in the 10 MHz output, which makes it look like a pretty crappy square wave. Of course there are higher harmonics.

How clean is the 'primary' 15MHz output, qualitatively or quantitatively?

The 15 MHz output is a very nice looking sign wave with the first harmonic down about 40dB. I don't have the means to measure phase noise.

As for a PCB for the 5MHz processing doubler and distribution amp, I could make some gerber files that would be compatible with OSHPark, Seeedstudio, elecrow, dirtypcbs, et. al. publically available in the near future if there is continued interest and I can get the CAD data on the particular parts involved in the publication.

I'd like to see if we can hear from some more knowledgeable folks on the relative benefits of deriving a 10 MHz sine using the circuit I posted a link to. I do like that it gives you a 4 channel distribution amplifier for free. I would find that useful in and of itself.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 12:41:36 am
If ths 15Mhz is created in the same way as the old one, you should be able yo bypass the the 15mhz filter as pass the 10mhz to the output amplifier.

I found a 10 Mhz sine signal that appears to be coming from a simple freq doubler which goes to a Schmitt trigger to get squared off that I think eventually comes out the 10 Mhz TP (J1). Think I will run that into some sort of driver and make that my 10 Mhz reference source rather than trying to filter the square wave.

How "clean" is the sign wave? Can you hook it up to a SA and see what it looks like?
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 29, 2015, 01:26:39 am
If ths 15Mhz is created in the same way as the old one, you should be able yo bypass the the 15mhz filter as pass the 10mhz to the output amplifier.

I found a 10 Mhz sine signal that appears to be coming from a simple freq doubler which goes to a Schmitt trigger to get squared off that I think eventually comes out the 10 Mhz TP (J1). Think I will run that into some sort of driver and make that my 10 Mhz reference source rather than trying to filter the square wave.
How "clean" is the sign wave? Can you hook it up to a SA and see what it looks like?

This is what I measured at U206.1 bottom side of board.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 05:02:10 am
Received my GearMo today and it works great ! Turns out my old 422 converter took a dump. Also ordered a cheaper converter that worked 1 time, yup, it has the counterfeit FTDI chip.

So far the receiver sees 9 birds and tracks 8 of them as compared to 12 out of 15 with something that was made in this past century and with an indoor antenna lol 

oh, the counterfeit FTDI works fine with the drivers that came with the unit on my Win XP machine but not Win 7. Guess you get what you pay for !
 
http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 (http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00)

Glad you got it all working. I made a proper DB9 cable for mine today, so no more terminal strip with wires hanging off it :)

I need to figure out how the DB9 power connection locks in. I read somewhere that the little pins (instead of screws) are called "slidelock". Have to see if I can get a connector with those.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 05:05:00 am
Received my GearMo today and it works great ! Turns out my old 422 converter took a dump. Also ordered a cheaper converter that worked 1 time, yup, it has the counterfeit FTDI chip.

So far the receiver sees 9 birds and tracks 8 of them as compared to 12 out of 15 with something that was made in this past century and with an indoor antenna lol 

oh, the counterfeit FTDI works fine with the drivers that came with the unit on my Win XP machine but not Win 7. Guess you get what you pay for !
 
http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00 (http://smile.amazon.com/gp/product/B00N9RCPAY?psc=1&redirect=true&ref_=oh_aui_detailpage_o01_s00)

Glad you got it all working. I made a proper DB9 cable for mine today, so no more terminal strip with wires hanging off it :)

I need to figure out how the DB9 power connection locks in. I read somewhere that the little pins (instead of screws) are called "slidelock". Have to see if I can get a connector with those.

Definitely not as pure a sine as the 15M, but I'm not sure that really matters. Maybe we should just create a little buffer amp for that - one that can drive 3 or 4 outputs. I like having a dist amp built into this thing. Do the hack to get rid of the REF-0, and you'd have a a lot more compact package.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 29, 2015, 07:30:51 am
The 15Mhz  doesnt look too bad from what I can see and I didnt realise the output was so hefty! Used 50db of attenuation when I made this sweep. I  think I will buffer the 5Mhz osc and mix them together ? 
Wish I could make some phase noise measurements but my HP 8591E isn't much better  :(
As far as distribution goes, rather than building one I might try a video distribution amp.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 29, 2015, 07:43:52 am
Glad you got it all working. I made a proper DB9 cable for mine today, so no more terminal strip with wires hanging off it :)

I need to figure out how the DB9 power connection locks in. I read somewhere that the little pins (instead of screws) are called "slidelock". Have to see if I can get a connector with those.
[/quote]

Why not just replace those with regular hardware ?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 11:07:06 am
I need to figure out how the DB9 power connection locks in. I read somewhere that the little pins (instead of screws) are called "slidelock". Have to see if I can get a connector with those.

Why not just replace those with regular hardware ?

Yeah, well, because then it's not in "pristine" condition :)
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 29, 2015, 03:28:14 pm
I'm assuming most of these posts are referring to the

LUCENT/SYMMETRICOM/HP Z3810AS, KS24361 L101 REF0 / L102 REF1, GPSDO TIMING SYSTEM

as shown. Maybe the thread name can reflect that?

Great stuff by the way...
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 29, 2015, 03:35:27 pm
I'm assuming most of these posts are referring to the

LUCENT/SYMMETRICOM/HP Z3810AS, KS24361 L101 REF0 / L102 REF1, GPSDO TIMING SYSTEM

as shown. Maybe the thread name can reflect that?

Great stuff by the way...

Yes, most, but there are plenty of posts about other options. I didn't want to change the thread title because When I have done that in the past, people end up dropping off the thread because they can't find it.
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 30, 2015, 04:44:30 am
I did follow some threads in the time-nuts history and looked at several other sites but I feel like I'm still scratching the surface for the information on these units.  And I understand there are several historical very similarly implemented (interfaces, command sets, software protocols or whatever) previous models in the series for which I've done little research yet.
So, at the risk of asking silly questions I'll pose these and will be hapy to go do more research if the detailed answers are well elucidated elsewhere.

(a) What are 'common' (where reported) failure modes for these units?

(b) Are there particular cautions about the care for and use of  these units that are important to understand moreso than general electronic equipment?  Bad ESD tolerance?  Bad vibration/shock tolerance? Don't tolerate being power cycled often?

(c) There was if I recall correctly in this thread some mention of some possibly related (older generation/model) units suddenly dying for no apparent reason.  Whether or not that's relevant to these units it made me wonder if there are 'ordinary' operations that are to be considered potentially dangerous.  For instance in normal industrial use maybe there is expected to be little use of the interactive diagnostics or command and control interfaces once the units are installed and tested / configured.  So perhaps using certain kinds of status queries or configuration commands causes the unit to write to FLASH for logging or reconfiguration or something.  Perhaps if extensive use was made of certain such commands one could conceivably burn out the flash storage or something like that.  For equipment like this I can understand the temptation to do something like run a continuous monitoring / inquiry scan maybe even continually at full speed or every several seconds or something.  What satellites are tracked?  What's the estimated error for timing now? What is the time? etc. etc.  So it occurred to me that maybe there are some "known safe" operations to use frequently and others that are known dangerous, and that such would be good to know before getting carried away doing software console or serial port / LAN interface based monitoring.

(d) For newly installed units obviously it is interesting and useful to poll a lot of status data about the unit's GPS status and timing stability and health and such.  What is the recommended way to gather such data to establish a history?  I can see the utility of writing some scripts to poll such information over the diagnostics / serial ports, though I don't know how often such polling is best done and which data queries are considered most useful if to be polled automatically.  As I recall there was a tip about a mode to output continuous status data automatically, though my first impression was that perhaps that was only a subset of the most useful data.  Suggestions?  I'd like to figure out how to monitor its 'break in' time of 90 days or so intensively (if safe) and then to monitor it automatically and in some reasonable detail at some useful rate thereafter.

(e) There have been complaints about the relative lack of sensitivity of the GPS receiver in these units relative to more modern designs.  I'm wondering if there's a suggested amount of gain and suggested noise figure of antenna system that is enough to get these units working as well as they can relative to other limitations in their receiver design.  I understand some 'cheap puck' antennas can give reasonably good performance if mounted away from any obstructions, though if an extra 15dB of gain or a lower NF is likely beneficial I'd like to know what is recommended.

(f) For units that have been well stabilized, is there much difference in the first 30-90+ days vs. long term for the crystals to stabilize and burn in?

(g) How long should I expect it to take a new unit to start performing at its full capacity given both initial OCXO burn in as well as slow tuning and such?

(h) Is there any harm in running only the unit with the GPS receiver in it disconnected from the secondary 'redundant' one if I only need the PPS and 15MHz or 5MHz or such outputs from the primary active unit?  Do I need to do something special with the cable to make it think the redundant unit exists but is in standby or has failed or something?  If I try this will I likely be filling up internal FLASH logs with continuous 'ALARM' / 'FAULT' records or something?

(i) Do these units recover well and automatically / quickly from having their antennae moved around within the boundaries of a single premises (but still enough meters of change to throw off some of the timing and such)?

Thanks in advance!
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 30, 2015, 06:23:50 am
evb, you ask a lot of questions!  But they're good questions, so here goes.

(a)  Common failure modes.  None that I've heard of.  Since these things are NOS, there might be some infant mortality, but I've heard that the seller is quite good about replacements.

(b)  Delicate equipment?  Hell, no!  They were made by HP for Lucent.  It doesn't get much better than that.  I have an older member of the family.  I've had it for a few years and it's been monitored continuously since I got it.  I suspect that most of the units in service with hobbyists are the same.  There was a question about whether the Z38xx program had a subtle bug that could wear out the EEPROM in the Z3801A and, by extension, other members of the family.  The author patched the program to remove that danger.

(c)  Dying for no reason.  No, that was a somewhat off-topic comment about a totally unrelated unit (Rockwell Jupiter GPS receiver).

(d)  Data collection.  Start with the program called Z38xx written by the late Ulrich Bangert.  Although it needs a hack to recognize these units, it's a minor thing.  If that program isn't to your taste, roll your own.  It's just a serial port.

(e)  Antennas.  Get a timing grade antenna.  Typically, they're bullet shaped rather than a puck.  The timing grade antennas have better filtering and typically higher gain than other types.  Make sure it will tolerate 5V.  Newer ones might be 3V3 only.  More definitive recommendations are difficult because local conditions like cable length and local signal obstructions will have an effect.  Earlier in the thread motocoder and I posted graphs and info on our setups.  That's as good a guide as any.

(f) and (g)  Initial vs. burned-in performance.  That's not clear.  I'm beginning to wonder just what their ultimate performance will be.  As we speak, I'm playing with yet another GPSDO from Trimble.  The performance is quite similar to the Lucent boxes we're discussing here.  But when I removed the OCXO from the board and measured it seperately, its short-term performance was much better than its short-term performance while on the board.  It seems that the board is reducing the OCXOs short-term performance while improving its long term performance.  There's no way to tell if that was intentional or irrelevent to the designers.  So until we hear from someone who has had these units online for a few months - and there should be some since they first came on the market late last year - we won't know what the ultimate performance will be.

But remember, I'm coming at it from the point of view of a slightly obsessed, PITA, time-nut who bitches and whines about a GPS receiver that has a 10 MHz output that's off by 0.00015 Hz!  For sane, normal people these units will perform perfectly well out of the box.

(h)  Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.

(i)  Reaction to moving a unit?  Anytime you move the antenna, you introduce some error into the system.  The error can show up as more jitter in the output or as jumps when a satellite joins or leaves the list of tracked birds.  Whether the error is significant will depend on your application.  In general, when you move the antenna, you should rerun the position survey.  I think there's a command for that, but I'm not sure.

 :phew:

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 30, 2015, 07:56:03 am
(h)  Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.

I found one person on time-nuts that described how this was done. It involved building a small circuit to toggle the values on inputs on J5 in response to certain outputs. His approach involved wiring into the signal on the Fault LED, so it wasn't an external-only solution.

(i)  Reaction to moving a unit?  Anytime you move the antenna, you introduce some error into the system.  The error can show up as more jitter in the output or as jumps when a satellite joins or leaves the list of tracked birds.  Whether the error is significant will depend on your application.  In general, when you move the antenna, you should rerun the position survey.  I think there's a command for that, but I'm not sure.

I believe you can start a survey with this command:

:PTIMe:GPSystem:POSition:SURVey:STATe ONCE

By default, the units are set up to do a survey on start-up. You can manually trigger a reset/start-up sequence with this command:

:SYSTem:PON

If you don't like the survey on start behavior, you can disable that with this command:

:GPSystem:POSition:SURVey:STATe:POWerup 0

More commands can be found here:
http://do-nyc.bodosom.net/ (http://do-nyc.bodosom.net/)
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 30, 2015, 01:11:31 pm
(h)  Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.

I found one person on time-nuts that described how this was done. It involved building a small circuit to toggle the values on inputs on J5 in response to certain outputs. His approach involved wiring into the signal on the Fault LED, so it wasn't an external-only solution.

I had vague memories that there was a 'version 2' of this mod so I did some digging.  Take a look at:

http://www.febo.com/pipermail/time-nuts/2014-November/087793.html (http://www.febo.com/pipermail/time-nuts/2014-November/087793.html) plus a half dozen or so messages after that.

Apparently you can just set up a jumper plug.

Somebody should set up a wiki for all the information on these boxes.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 30, 2015, 01:19:35 pm
Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.
I found one person on time-nuts that described how this was done. It involved building a small circuit to toggle the values on inputs on J5 in response to certain outputs. His approach involved wiring into the signal on the Fault LED, so it wasn't an external-only solution.

Or even better than that, read what is discussed here:
http://www.febo.com/pipermail/time-nuts/2014-November/087972.html (http://www.febo.com/pipermail/time-nuts/2014-November/087972.html)

Which indicates that the GPS unit J5 Pin 2 requires a 470ohm pull down resistor to ground (pin 8 or pin 13) and pin 3 requires wiring directly to ground. As far as I'm aware the numbering is right to left looking at the unit front on. Please double check this yourself.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 30, 2015, 01:42:01 pm
As for a PCB for the 5MHz processing doubler and distribution amp, I could make some gerber files that would be compatible with OSHPark, Seeedstudio, elecrow, dirtypcbs, et. al. publically available in the near future if there is continued interest and I can get the CAD data on the particular parts involved in the publication.

I would like to see a 10Mhz out for the Z3811A or a cleaner 10MHz signal for the Z3812A, I have 16 port distribution amp already so I'm a little against the need for adding a large distribution modification to the Z3811A.

As there is so far a rear power supply mod, standalone Z3811A mod, Z3811A GPS backup battery mod, I think a single 10Mhz output (with 1pps if required) on the rear of the Z3811A seems the best idea.

Drilling multiple holes in the face seems to be over engineering it and butchering what could otherwise be a very discrete modification.

If someone comes out with a minimalist approach I'm interested in adding the PCB and modding mine.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 30, 2015, 01:46:08 pm
(h)  Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.

I found one person on time-nuts that described how this was done. It involved building a small circuit to toggle the values on inputs on J5 in response to certain outputs. His approach involved wiring into the signal on the Fault LED, so it wasn't an external-only solution.

I had vague memories that there was a 'version 2' of this mod so I did some digging.  Take a look at:

http://www.febo.com/pipermail/time-nuts/2014-November/087793.html (http://www.febo.com/pipermail/time-nuts/2014-November/087793.html) plus a half dozen or so messages after that.

Apparently you can just set up a jumper plug.

Somebody should set up a wiki for all the information on these boxes.

Ed

Maybe we could just add a page on Wikipedia?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 30, 2015, 01:50:23 pm
Run one unit only?  There was discussion on that, but since I got these as spares, I haven't investigated.  You should be able to find the info on time-nuts.
I found one person on time-nuts that described how this was done. It involved building a small circuit to toggle the values on inputs on J5 in response to certain outputs. His approach involved wiring into the signal on the Fault LED, so it wasn't an external-only solution.

Or even better than that, read what is discussed here:
http://www.febo.com/pipermail/time-nuts/2014-November/087972.html (http://www.febo.com/pipermail/time-nuts/2014-November/087972.html)

Which indicates that the GPS unit J5 Pin 2 requires a 470ohm pull down resistor to ground (pin 8 or pin 13) and pin 3 requires wiring directly to ground. As far as I'm aware the numbering is right to left looking at the unit front on. Please double check this yourself.

Ah, I saw this post before. Near the end of the message, he decides the connection to Pin 2 isn't needed:

Quote
...all that's needed to enable a Ref-1 unit stand alone is to link together J5 pins 2, 10, 12,  and 15, and to ground pin 3 to pin 8, and then just hang around for hours and  hours on end with yer fingers crossed:-)

And I THINK in a later reply he decides the connection to pin 3 should be a pull down resistor instead of a direct short to ground. I'll have to double-check that as I know you have to be careful about having both pull-ups and pull-downs attached to a CMOS circuit.

What does he mean when he says this: "When pin 5 and pin 11 are  observed together, the usual GPS sawtooth pattern is  evident."

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 30, 2015, 01:52:14 pm
As for a PCB for the 5MHz processing doubler and distribution amp, I could make some gerber files that would be compatible with OSHPark, Seeedstudio, elecrow, dirtypcbs, et. al. publically available in the near future if there is continued interest and I can get the CAD data on the particular parts involved in the publication.

I would like to see a 10Mhz out for the Z3811A or a cleaner 10MHz signal for the Z3812A, I have 16 port distribution amp already so I'm a little against the need for adding a large distribution modification to the Z3811A.

As there is so far a rear power supply mod, standalone Z3811A mod, Z3811A GPS backup battery mod, I think a single 10Mhz output (with 1pps if required) on the rear of the Z3811A seems the best idea.

Drilling multiple holes in the face seems to be over engineering it and butchering what could otherwise be a very discrete modification.

If someone comes out with a minimalist approach I'm interested in adding the PCB and modding mine.

I think you make a good point. How about just modding it so the 15 MHz SMA connector becomes a 10 MHz output?
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 30, 2015, 03:42:16 pm
As of June 19, eLoran is on the air in the United States. The low-frequency signal emanates from a single station, a former U.S. Coast Guard Loran Unit in Wildwood, N.J., which sports a 625-foot signal mast that has been out of action for five years. The signal is receivable at distances of up to 1,000 miles.

If you already own a receiver,(in that area) well, could be economical...
http://gpsworld.com/eloran-progresses-toward-gps-back-up-role-in-u-s-europe/ (http://gpsworld.com/eloran-progresses-toward-gps-back-up-role-in-u-s-europe/)


Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on July 30, 2015, 03:53:06 pm


Nigel, and I worked on this project to get the Stanford Research FS-700 manual complete with schematics up on K04bb.
I provided high resolution copies, and he organized, and collected it all into one pdf. I then uploaded onto K04bb.
He mentions good prices on the FS-700, but they recently have gone through the roof! Not sure why yet...

https://www.febo.com/pipermail/time-nuts/2015-July/092812.html (https://www.febo.com/pipermail/time-nuts/2015-July/092812.html)
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 31, 2015, 08:06:37 am
Thanks for the great information all!
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on July 31, 2015, 08:32:37 am
I wanted to see how close the Lucent RFTG unit is compared to Nortel Trimble NTBW50AA Thunderbird unit. Both units using the same antenna over a 3 hour time period.  Triggering on Ch 1 (Lucent) yellow trace and Ch 2 is the 10 Mhz TP output from the RFTG unit with the scopes persistence set to infinity.
Forgive the crappy pic, am tiered and cant see straight lol

Title: Re: Economical option for precision frequency reference?
Post by: Shock on July 31, 2015, 12:50:50 pm
I would like to see a 10Mhz out for the Z3811A or a cleaner 10MHz signal for the Z3812A, I have 16 port distribution amp already so I'm a little against the need for adding a large distribution modification to the Z3811A.
As there is so far a rear power supply mod, standalone Z3811A mod, Z3811A GPS backup battery mod, I think a single 10Mhz output (with 1pps if required) on the rear of the Z3811A seems the best idea.
Drilling multiple holes in the face seems to be over engineering it and butchering what could otherwise be a very discrete modification.
If someone comes out with a minimalist approach I'm interested in adding the PCB and modding mine.

I think you make a good point. How about just modding it so the 15 MHz SMA connector becomes a 10 MHz output?

All depends how much modification it requires, am still reading through the time-nut posts.

I prefer everything out the back and mount just the GPS unit in an enclosure rather than a rack.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on July 31, 2015, 01:43:47 pm
I would like to see a 10Mhz out for the Z3811A or a cleaner 10MHz signal for the Z3812A, I have 16 port distribution amp already so I'm a little against the need for adding a large distribution modification to the Z3811A.
As there is so far a rear power supply mod, standalone Z3811A mod, Z3811A GPS backup battery mod, I think a single 10Mhz output (with 1pps if required) on the rear of the Z3811A seems the best idea.
Drilling multiple holes in the face seems to be over engineering it and butchering what could otherwise be a very discrete modification.
If someone comes out with a minimalist approach I'm interested in adding the PCB and modding mine.

I think you make a good point. How about just modding it so the 15 MHz SMA connector becomes a 10 MHz output?

All depends how much modification it requires, am still reading through the time-nut posts.

I prefer everything out the back and mount just the GPS unit in an enclosure rather than a rack.

If you keep reading the time-nuts thread on standalone operation of REF-1, eventually you find this post:

https://www.febo.com/pipermail/time-nuts/2014-November/088043.html (https://www.febo.com/pipermail/time-nuts/2014-November/088043.html)

Which describes a mod that can be done, entirely via an adapter plugged into J5, to allow REF-1 to operate in standalone mode. Since REF-1 does not have a 10 MHz output, you will obviously also have to do something there. The adapter is:

      470R
2 ---/\/\/\---8/13
3 ----------- 8/13


I.e. short pin 3 directly to ground (available on either pin 8 or 13), pull down pin 2 to ground via a 470 ohm resistor.I haven't tried it to verify, but I believe they are saying that it can take an hour for REF-1 to come up in "ON" mode with the 15 MHz and 1PPS outputs enabled when using this adapter.

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on July 31, 2015, 03:54:53 pm
I wanted to see how close the Lucent RFTG unit is compared to Nortel Trimble NTBW50AA Thunderbird unit. Both units using the same antenna over a 3 hour time period.  Triggering on Ch 1 (Lucent) yellow trace and Ch 2 is the 10 Mhz TP output from the RFTG unit with the scopes persistence set to infinity.
Forgive the crappy pic, am tiered and cant see straight lol

Okay, but what does that mean?  Every GPSDO has jitter.  You'd see something similar if you compared two identical units.  Also, your measurement technique makes it look like the Nortel unit is perfect and all the jitter is on the Lucent unit when they're actually both jittering around.

In the past I measured the jitter of the 1 PPS output of a few bare GPS receivers and GPSDOs.  Here are the results:

GPS Devices -- Performance of 1 PPS Output

Device ............... Std Dev (ns).... Range (max-min)(ns) ... Device Type

Navsync CW12 ......... 4 - 5 .......... 20 - 25 ............... GPS Rcvr (1) see below
Motorola UT+ ......... 40 - 55 ........ 95 - 110 .............. GPS Rcvr (2)
Rockwell Jupiter ..... 10 ............  50 ...................  GPS Rcvr (3)
Motorola M12M ........ 10 - 15 ........ 40 - 60 ............... GPS Rcvr

Trimble Thunderbolt .. 0.4 - 0.5 ...... 2 - 4 ................. GPSDO
HP Z3801A ............ 0.1 - 0.2 ...... < 1 ................... GPSDO   
HP Z3817A / CW12 ..... < 0.1 .......... < 1 ................... GPSDO    (4)
Jackson Labs GPSTCXO . 0.3 - 0.4 ...... 2 - 3 ................. GPSDO


Results are based on multiple runs of ~ 1000 measurements each.
Sawtooth correction has not been used for any of the GPS receivers.  Where supported, it would reduce the numbers substantially.
GPS Rcvr measurements made with HP 5372A.  GPSDO measurements made with HP 5370B.
All units were connected to the same antenna system.

1.  Sawtooth correction not supported.
2.  Most 'range' results were in this group, but there were a few at 20 - 30.
3.  Only one test.
4.  Requires external 1 PPS input.  Equipped with E1938 oscillator.



I haven't done these tests on the RFTG-u.  I'll have to add it to the list.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on July 31, 2015, 05:09:24 pm
I haven't looked at the details fully but that photograph looks like there was quite a lot of phase variation relative to the entire 10MHz cycle, which surprised me.  I would have expected the jitter to be visible only on one zoomed in edge of the waveforms and to account for a small fraction of a cycle's phase over a relatively short (hour) interval with there being a bit of phase noise with an underlying phase drift progression due to the frequency discord.

I also wonder about whether the clock outputs wouldn't get cleaner wrt. jitter during GPS LOS periods since there is no further input for the corrections.  Of course I suspect the devices create a mathematical model of a given OCXO's 'inherent' frequency error and temperature sensitivity and may try to keep correcting for the predicted error according to the trained model data (and perhaps also temperature measurement though probably not if it is assumed to simply be stable in the oven's feedback).  But eventually I suppose the 'remembered' feedback due to the frequency error modem might 'age out' and then one would be left with basically the OCXO's intrinsic output given the temperature / power supply / noise related fluctuations.
Or I suppose if you cold started a unit and could get it to output the 15MHz or 10MHz or whatever without having the GPS related corrections enabled due to insufficient data to model the OCXO error at which point you'd be left with less control system jitter, though it may simply not output the high frequency at such a time.  I recall seeing something about a fault described in the RFTG's SW report descriptions as 'flywheel failed, duration > 8 hr' so I wasn't sure what it'd do wrt. HF output after 8hr or 24hr in flywheel.

I suppose it might also be possible to trick the non-GPS RFTG unit into giving 'pure' OCXO output by doing something like feeding its own 15MHz output divided by 15M back into its PPS reference input as if that was coming from the GPS disciplining unit, I suppose one might need to do some phase adjustment to get it to accept that there was a 0 static phase error in that process.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 12:30:17 am
I haven't looked at the details fully but that photograph looks like there was quite a lot of phase variation relative to the entire 10MHz cycle, which surprised me.  I would have expected the jitter to be visible only on one zoomed in edge of the waveforms and to account for a small fraction of a cycle's phase over a relatively short (hour) interval with there being a bit of phase noise with an underlying phase drift progression due to the frequency discord.

I also wonder about whether the clock outputs wouldn't get cleaner wrt. jitter during GPS LOS periods since there is no further input for the corrections.  Of course I suspect the devices create a mathematical model of a given OCXO's 'inherent' frequency error and temperature sensitivity and may try to keep correcting for the predicted error according to the trained model data (and perhaps also temperature measurement though probably not if it is assumed to simply be stable in the oven's feedback).  But eventually I suppose the 'remembered' feedback due to the frequency error modem might 'age out' and then one would be left with basically the OCXO's intrinsic output given the temperature / power supply / noise related fluctuations.
Or I suppose if you cold started a unit and could get it to output the 15MHz or 10MHz or whatever without having the GPS related corrections enabled due to insufficient data to model the OCXO error at which point you'd be left with less control system jitter, though it may simply not output the high frequency at such a time.  I recall seeing something about a fault described in the RFTG's SW report descriptions as 'flywheel failed, duration > 8 hr' so I wasn't sure what it'd do wrt. HF output after 8hr or 24hr in flywheel.

I suppose it might also be possible to trick the non-GPS RFTG unit into giving 'pure' OCXO output by doing something like feeding its own 15MHz output divided by 15M back into its PPS reference input as if that was coming from the GPS disciplining unit, I suppose one might need to do some phase adjustment to get it to accept that there was a 0 static phase error in that process.

The microprocessor in the unit is making EFC corrections periodically to keep the thing in sync with the GPS signal. I can see in the reported PPS stats that the PPS value is varying between about +/- 40ns of the GPS time, and for others here, whose units arent' quite as well behaved, it's more like +/-90ns. The o-scope capture posted earlier was I assume taken by turning on infinite persistence on the scope and letting it run for 3 hours. So I would entirely expect this sort of display as the EFC value gets updated many times over that 3 hour span.
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on August 01, 2015, 03:12:53 am
Interesting.  That is quite a lot of jitter for some of the units (40-90ns).  Particularly out of a 100ns period 10MHz cycle anything more than 1ns of jitter is relatively speaking a lot (3.6 degrees / ns @ 10MHz).

BTW I looked at the data from KO4BB's site but I still haven't seen anything like an output specification for the 15MHz or PPS signals, is there a published value for what the frequency accuracy and jitter and such are supposed to be when the unit is operating normally?

As I understand it the PPS signals for timing oriented equipment are actually supposed to be synchronous with the transition of the GPS referenced second's transition time, generally down to nanoseconds levels of precision.  I'm not sure that the RFTG units are oriented toward "timekeeping" so much as an accurate long term stable frequency reference at 1Hz and 15MHz though I suppose they probably also keep the clock edge of the PPS relatively aligned to the actual transition of the second though it sounds like that is only to the level of ~40ns to ~90ns which really sounds like it is about a half cycle of the 5MHz crystal clock.
Though it is odd if it can flywheel for 24hrs with microseconds of drift accuracy and still get large fractions (90ns) of that as short term corrections.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 06:48:29 am
Interesting.  That is quite a lot of jitter for some of the units (40-90ns).  Particularly out of a 100ns period 10MHz cycle anything more than 1ns of jitter is relatively speaking a lot (3.6 degrees / ns @ 10MHz).

BTW I looked at the data from KO4BB's site but I still haven't seen anything like an output specification for the 15MHz or PPS signals, is there a published value for what the frequency accuracy and jitter and such are supposed to be when the unit is operating normally?

As I understand it the PPS signals for timing oriented equipment are actually supposed to be synchronous with the transition of the GPS referenced second's transition time, generally down to nanoseconds levels of precision.  I'm not sure that the RFTG units are oriented toward "timekeeping" so much as an accurate long term stable frequency reference at 1Hz and 15MHz though I suppose they probably also keep the clock edge of the PPS relatively aligned to the actual transition of the second though it sounds like that is only to the level of ~40ns to ~90ns which really sounds like it is about a half cycle of the 5MHz crystal clock.
Though it is odd if it can flywheel for 24hrs with microseconds of drift accuracy and still get large fractions (90ns) of that as short term corrections.

It's not 40 - 90ns of jitter on a waveform at 10 MHz (100ns). It's 40-90ns delta over the GPS reference over a 1 second interval. The hardware has no mechanism to measure jitter over a individual periods of the 10Mhz clock. What it does it count the number of 10 MHz (probably 5 Mhz in this case - but let's use 10MHz for simplicity of discussion) OCXO cycles that occur from one GPS PPS rising edge to the next GPS PPS rising edge. If the count is 9,999,996, it calculates that it's -40ns relative to GPS, and it uses this value as an error signal into the PID loop that is controlling the EFC voltage. Similarly, if the count is 10,000,009, it calculates that it's 90ns relative to the GPS, feeds that into the PID loop, and adjusts the EFC accordingly.

Regarding the stability over the course of the day, I suspect it estimates this based on some calculation involving the rate of change of EFC and the standard deviation or variance of frequency when in closed-loop mode (GPS tracking active). The theory being that if it goes into an open-loop mode (no GPS), it will leave the EFC voltage at a constant value, and the drift in frequency will be a function of how much it was having to change EFC previously and how much the frequency was varying even when EFC was tightly controlled.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 02:44:48 pm
I have uncovered a couple of interesting data points on my Lucent unit.

1) I noticed that the PPS fluctuations seemed to increase every time the A/C turned on here. So I put a small 12V fan behind the unit blowing air through at a very low CFM rate. Notably, this seemed to cause the fluctuations to get worse. I observed this over many hours, and as soon as I removed the fan, it returned to the previous pattern.
2) After removing the fan, I put a  piece of cardboard around the A/C vent so that the air would not circulate past the Lucent unit as much. This settled things way down, and the PPS value seems to mostly be +/- 10ns with occasional excursions to +/- 20ns and a much rarer spike to +/-30 ns.

During #2, the HUD value started to go down for awhile, but then started increasing again. It appears strongly correlated with the rate of change of the EFC value, which was fairly steady for a short time (while HUD was decreasing), but then started to rise again.

So in conclusion, the unit is sensitive to the environmental air temperature and possibly the EMI generated by that fan. The HUD value seems to be strongly correlated with the rate of change of EFC. The more constant EFC is when the unit is locked to GPS, the lower the HUD value, regardless of how much "jitter" there is of PPS.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 01, 2015, 03:17:07 pm
I have uncovered a couple of interesting data points on my Lucent unit.

1) I noticed that the PPS fluctuations seemed to increase every time the A/C turned on here. So I put a small 12V fan behind the unit blowing air through at a very low CFM rate. Notably, this seemed to cause the fluctuations to get worse. I observed this over many hours, and as soon as I removed the fan, it returned to the previous pattern.
2) After removing the fan, I put a  piece of cardboard around the A/C vent so that the air would not circulate past the Lucent unit as much. This settled things way down, and the PPS value seems to mostly be +/- 10ns with occasional excursions to +/- 20ns and a much rarer spike to +/-30 ns.

During #2, the HUD value started to go down for awhile, but then started increasing again. It appears strongly correlated with the rate of change of the EFC value, which was fairly steady for a short time (while HUD was decreasing), but then started to rise again.

So in conclusion, the unit is sensitive to the environmental air temperature and possibly the EMI generated by that fan. The HUD value seems to be strongly correlated with the rate of change of EFC. The more constant EFC is when the unit is locked to GPS, the lower the HUD value, regardless of how much "jitter" there is of PPS.

I noticed that mine reacted strongly when a stray sunbeam fell on it for a few minutes.  I'm surprised that a double-oven OCXO would be that sensitive to external thermal influences.  The high number of holes in the case suggests that when these units were in service there was a fan tray or something similar that flooded the entire bay with a continuous stream of air to maintain a constant temperature.  Closing off those holes would have to be done cautiously to make sure that nothing was going to overheat, but reducing drafts on the oscillator would likely improve performance.

By the way, don't add extra insulation around the OCXO!  The internal heat must be allowed to escape.  If you prevent that, the oven controller won't be able to control the temperature properly.  Worst case, the internal temperature starts to rise and the unit cooks itself.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 05:01:55 pm
I noticed that mine reacted strongly when a stray sunbeam fell on it for a few minutes.  I'm surprised that a double-oven OCXO would be that sensitive to external thermal influences.  The high number of holes in the case suggests that when these units were in service there was a fan tray or something similar that flooded the entire bay with a continuous stream of air to maintain a constant temperature.  Closing off those holes would have to be done cautiously to make sure that nothing was going to overheat, but reducing drafts on the oscillator would likely improve performance.

Yes, my theory on this is that we're talking about such minute changes in frequency, that even a tiny outside temperature change can have an effect. I wish I had some other unit to compare against - not sure if this is normal. Do you think the stray sunbeam was impacting the outside temperature of the oven, or is there perhaps some chip-scale IC inside these units?

BTW, I found an interesting paper from Milliren on crystal oscillator aging: http://www.mti-milliren.com/MTIPapers/Ext_Aging_Perf_Results.pdf (http://www.mti-milliren.com/MTIPapers/Ext_Aging_Perf_Results.pdf)

By the way, don't add extra insulation around the OCXO!  The internal heat must be allowed to escape.  If you prevent that, the oven controller won't be able to control the temperature properly.  Worst case, the internal temperature starts to rise and the unit cooks itself.

Noted. Thanks
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 01, 2015, 05:23:05 pm
Yes, my theory on this is that we're talking about such minute changes in frequency, that even a tiny outside temperature change can have an effect. I wish I had some other unit to compare against - not sure if this is normal. Do you think the stray sunbeam was impacting the outside temperature of the oven, or is there perhaps some chip-scale IC inside these units?

You mean like the RPi a few months back?  I think these units are too old for that.  If I remember correctly, it took the unit several minutes to recover after I blocked the sunbeam so I think it was a thermal effect.

I have a Z3801A which is equipped with an HP double-oven oscillator.  The oscillator is surprisingly crude for an HP unit.  They basically took an HP 10811 oscillator (really good reputation, by the way), made a few internal changes to increase the electrical tuning range, and then wrapped another heater and insulation around it.  There are autopsy photos online.  Once you dig out the oscillator, it even has the original label on it.  In spite of how crude it is, it works quite well.  The entire unit is in a solid steel box with a reasonable number of slots for cooling.  Thermal changes don't really bother it - even at these tiny levels.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 05:43:40 pm
Yes, my theory on this is that we're talking about such minute changes in frequency, that even a tiny outside temperature change can have an effect. I wish I had some other unit to compare against - not sure if this is normal. Do you think the stray sunbeam was impacting the outside temperature of the oven, or is there perhaps some chip-scale IC inside these units?

You mean like the RPi a few months back?  I think these units are too old for that.  If I remember correctly, it took the unit several minutes to recover after I blocked the sunbeam so I think it was a thermal effect.

I have a Z3801A which is equipped with an HP double-oven oscillator.  The oscillator is surprisingly crude for an HP unit.  They basically took an HP 10811 oscillator (really good reputation, by the way), made a few internal changes to increase the electrical tuning range, and then wrapped another heater and insulation around it.  There are autopsy photos online.  Once you dig out the oscillator, it even has the original label on it.  In spite of how crude it is, it works quite well.  The entire unit is in a solid steel box with a reasonable number of slots for cooling.  Thermal changes don't really bother it - even at these tiny levels.

I wonder why these Lucent units are so recommended on Time-Nuts. There seem to be a lot of compromises to them: 15 Mhz sine instead of 10, "dirty" 10 MHz output only available on redundant unit, low sensitivity 8-channel GPS, funky connectors  (power and others), ... And so far the performance does not seem to match the alternatives out there. Am I missing something here?

BTW - my HUD has now risen to 6.5us. It was as low as 1.9us at one point. Not sure what's causing this? Maybe this is a normal pattern as the crystal breaks in?

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 01, 2015, 07:12:49 pm
I wonder why these Lucent units are so recommended on Time-Nuts. There seem to be a lot of compromises to them: 15 Mhz sine instead of 10, "dirty" 10 MHz output only available on redundant unit, low sensitivity 8-channel GPS, funky connectors  (power and others), ... And so far the performance does not seem to match the alternatives out there. Am I missing something here?

BTW - my HUD has now risen to 6.5us. It was as low as 1.9us at one point. Not sure what's causing this? Maybe this is a normal pattern as the crystal breaks in?

If you want, you can go out and buy a brand new, shiny GPSDO with a 50 channel receiver that can hear a whisper from another planet.  You probably don't want to know the price!

In the past, we were spoiled by units like the Trimble Thunderbolt and the other members of the Z38 series.  Their performance is amazing.  The Z3801 has a 6 channel receiver that needs a bit higher level.  So what?  It works great!  The Thunderbolt only has an eight channel receiver.  It doesn't need any more.

I don't think it's fair to say that the Lucent units were 'recommended' on the Time-Nuts mailing list.  It wasn't discussed, but I suspect that people were hoping that these units would have similar performance to the Thunderbolt and other Z38xx units which are now either unavailable or uneconomical.  They have good names behind them, a good pedigree and, of course, they were reasonably priced.  Most of the chatter on Time-Nuts involved the reverse-engineering process and modifications to make the unit more time-nut-friendly.  That's part of the fun!  Until the units ran for an extended period, there was no way to know what its ultimate performance would be.  I suspect that there's some disappointment within the list, but not enough to cause outright bitching and moaning.  After all, these are surplus units rather than new and they were priced accordingly.  They were just designed with different parameters than the Thunderbolt and the other Z38xx units.

The HUP will wander around a lot - particularly while the crystal is breaking in.  On my well-broken-in Z3801, there's an interesting oscillation in the HUP.  It goes from a high of 3 to 4 us down to a low of < 500 ns and back up.  The period of this oscillation is about 7 days!  This oscillation isn't visible on any other parameter in the box.  I haven't attempted to get to the bottom of it.  It seems like HUP values in the 5 us range are not surprising and there's significant unit-to-unit variability - probably determined by the characteristics of the particular OCXO in the unit.

These units do exactly what they claim.  They provide an absolute frequency and time reference that's traceable to international standards and are within the reach of any hobbyist.  For the majority of users, any imperfections will be irrelevant.  If you're not satisfied with their performance, well, I guess that means you're a Time-Nut, too!   ;)

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 07:51:13 pm
I was just curious where the performance of this unit is going to end up relative to the Thunderbolt. ANd I don't agree that people weren't recommending these units on the time-nuts mailing list. I went through literally every post on this unit in the archives, and there are several occasions where someone there recommends the unit.  I think the performance is fine for my needs - like I said, it's already paid for itself by calibrating my 53131A.

I do have some remaining work to do to get the antenna into a permanent location. Not looking forward to crawling around on the roof...
Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on August 01, 2015, 09:50:13 pm
Rather than venture onto the roof, one (lazy) option would be to just dig it out once every 6 months (or once a year) to calibrate your counter if it now has the high stability OCXO option fitted.

I've got numerous bits of RF test gear that contain a high stability OCXO option and I've just gone round several of my signal generators and the OCXO in each is still within 0.02Hz of 10MHz. This is a much better result than I was expecting because at least one of the generators hasn't been adjusted for a year or so.

I usually find that my various OCXOs stay within 0.1Hz of 10MHz over 6 months although I've only had one of these (used Agilent) generators for about 8 months and the other one for about 18months so this is new data. The other one I tested was a Marconi 2024 and this hasn't been adjusted for ages because it requires a fiddly menu/password access routine. I suspect there may be an element of luck in the fact that it is still within 0.02Hz of 10MHz as I've had this generator several years and it usually drifts a bit more than this over a year or so.

The huge and expensive Toyocom OCXO in my Anritsu counter was also within about 0.01Hz of 10MHz but I think I adjusted it back in January.

If you fit an external antenna on the rooftop will you be leaving the GPSDO running 24/7?  I don't leave my OCXOs running 24/7 and the generators just get used as and when required and they still seem to perform well. Although they are all  >10 years old and the 2024 Marconi must be >18 years old.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 01, 2015, 10:30:27 pm
Rather than venture onto the roof, one (lazy) option would be to just dig it out once every 6 months (or once a year) to calibrate your counter if it now has the high stability OCXO option fitted.

Unfortunately, the Lucent wasn't even able to acquire a lock on a single satellite when the antenna was indoors next to the window. So that means every time I would go to set it up, I'd have to temporarily mount the antenna outside somewhere, and run the cable through the window. Not a huge big deal, but it's another factor in the decision on whether or not to permanently set up an antenna.

If you fit an external antenna on the rooftop will you be leaving the GPSDO running 24/7?  I don't leave my OCXOs running 24/7 and the generators just get used as and when required and they still seem to perform well. Although they are all  >10 years old and the 2024 Marconi must be >18 years old.

I was thinking of just leaving the Lucent GPSDO running 24/7, and connecting the external reference on the other test gear to that via some sort of distribution amplifier (there are a number of them available for cheap on eBay). I definitely don't want more than one OCXO running, as they generate a fair bit of heat. I'd also like to not have to lave that 53131A on as it runs the fan continuously. I've set up a remote switch for it currently so that I can shut it off when not in use. Having the external reference means I wouldn't have to wait for anything to warm up.

But setting up the antenna is a big task, as I have to set up lightning suppression, grounding, and a wife-approved method to get the coax into the house. I know what to do there, but it's quite a bit of work.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 01, 2015, 11:08:14 pm
@ GOHZU , do you happen to know the model of your epson  oscillator?
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 02, 2015, 03:00:34 am
in comparison to my bg7tbl (oscilloquartz ocxo + ublox gps), the lucent is deaf. receiver sensitivity is abysmal and synchronization is extremely slow. like motocoder, i had to run an antenna outside to get it to work. it absolutely would not sync with the antenna inside a window. the 10mhz output is extremely distorted, and if you want to talk to it you have to jump through rs422 hoops. you even have to hack up a db9 power connector. ugh. you also have to source your own gps antenna. each unit sucks about 12W while running, so 24W total if you want to run the setup as designed. also due to its age, the lucent knows nothing about WAAS. the lucent is maybe 8 channels max.

very NOT recommended.

get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.
Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on August 02, 2015, 01:38:31 pm
@ GOHZU , do you happen to know the model of your epson  oscillator?

Can you clarify which one you mean?

I've got several Agilent instruments here with the 1E5 option OCXO but I've never tried to open up the OCXO module on any of them so I don't know who actually makes this OCXO or what the model number is. Apart from that I don't think any of my other OCXOs are made by Epson.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 02, 2015, 02:58:14 pm
The one in your anritsu counter,specs will suffice.
Title: Re: Economical option for precision frequency reference?
Post by: G0HZU on August 02, 2015, 04:00:16 pm
In my Anritsu counter there is a Toyocom OCXO and I think it's a special version of their old 615 range. These are big old OCXOs 50mm x 50mm x 60mm high and they take a long time to warm up.

I think the yearly ageing rate is <1.5e-8 and over temperature is < 5e-9 over 0 to 50degC. But I really don't like this OCXO because it takes so long to warm up. To get even basic settling takes about 50 minutes. i.e. this is how long it takes to allow the first overshoot and then undershoot and get to within 0.1Hz of 10MHz. There's a similar looking 615 series OCXO in my Advantest analyser but this warms up much faster even though it is the same package etc.

So I really don't recommend the OCXO in my counter even though it performs quite well apart from the slow warmup. I rarely need to use a counter these days but I usually use this counter with an external OCXO with very fast warmup. i.e. my Quintenz or my MFC OCXO that has almost the same spec but can warm up in well under 5 minutes :)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 02, 2015, 04:44:52 pm
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.

Have you seen a write-up on either of these units? The Trimble board actually says "Designed in the US" on the board. I am curious where it comes from, and how it performs relative to the other unit you mention, which I think is just the BG7TBL design with a different OCXO.
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 02, 2015, 05:55:04 pm
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.

Have you seen a write-up on either of these units? The Trimble board actually says "Designed in the US" on the board. I am curious where it comes from, and how it performs relative to the other unit you mention, which I think is just the BG7TBL design with a different OCXO.

the oscilloquartz board is a surplus gpsdo that comes out of some huawei telco equipment. it uses the exact same bg7tbl adapter board as the trimble. it's not just an ocxo swap.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 02, 2015, 06:14:42 pm
get a bg7tbl with oscilloquartz (2015-07-08) or trimble (2015-07-17) sub-board. you'll have a much more compact unit that uses much less power, much more sensitive and capable gps receiver, rs232, and true sine output. he even throws in a psu and gps antenna. it has no problem with the antenna inside the same window the lucent refused to work from.

Have you seen a write-up on either of these units? The Trimble board actually says "Designed in the US" on the board. I am curious where it comes from, and how it performs relative to the other unit you mention, which I think is just the BG7TBL design with a different OCXO.

the oscilloquartz board is a surplus gpsdo that comes out of some huawei telco equipment. it uses the exact same bg7tbl adapter board as the trimble. it's not just an ocxo swap.

Any data or opinions on the relative merits of the two boards? Is one better than another?

What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 02, 2015, 08:15:08 pm
I wrote little program that communicates over the serial port to pull the TI value from the Lucent every second. I was curious how frequently this value gets updated.

My Lucent is mostly reporting +/- 10ns values, with occasional excursions to as high as 50ns. Notably the value never changes at an interval of less than 10 seconds. So I wonder if actually this value is the deviation over a 10 second interval. I wish I  had a way to measure this.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 03, 2015, 12:18:55 am
You know, I just don't believe these TI numbers. Perhaps I don't understand what they represent. I hooked up the Lucent GPSDO 10MHz output to my 53131A, which has its own OCXO that has been calibrated to the Lucent.

Now if the Lucent was really drifting by 10 - 50ns per 1 second interval, unless the timer OCXO was drifting in sync (impossible), I would expect to see variation in the 0.1Hz digit. Instead, it is rock solid all the way out to the 0.0001 digit.

I guess maybe I need to sign up for the time-nuts mailing list and ask someone to explain it (or maybe Ed can explain here).
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 03, 2015, 03:47:34 am
You know, I just don't believe these TI numbers. Perhaps I don't understand what they represent. I hooked up the Lucent GPSDO 10MHz output to my 53131A, which has its own OCXO that has been calibrated to the Lucent.

Now if the Lucent was really drifting by 10 - 50ns per 1 second interval, unless the timer OCXO was drifting in sync (impossible), I would expect to see variation in the 0.1Hz digit. Instead, it is rock solid all the way out to the 0.0001 digit.

I guess maybe I need to sign up for the time-nuts mailing list and ask someone to explain it (or maybe Ed can explain here).

Believe your counter.  The GPSDO is reporting the TI between its PPS and the calculated PPS based on the received signals.  Problem is, the received signal gets distorted by the ionosphere and maybe by multipath.  This creates jitter in the calculated result.  Over a long period, this jitter averages out to zero.  The OCXO's function is to act as a flywheel to filter out the short-term jitter.  The  PPS is then generated from the OCXO.  The 'gotcha' here is that in the RFTG, the averaging appears to degrade the OCXO's performance - or doesn't completely filter out the short-term jitter.

There are a few things that can be checked to ensure that the jitter is minimized.  Like they say, "Location, location, location".  If the GPSDO doesn't have its location figured correctly, this can be a major cause of jitter.  I don't remember if the RFTG has this feature, but some GPSDOs give you the option to set the length of time for the location survey.  Longer is better!  The survey is just as vulnerable to jitter as the PPS.  A longer survey helps average out the jitter.  Give it a day or two - compare the before and after results. 

Note that measuring the output with a frequency counter isn't a very precise measurement because the counter's gate time results in an averaging function that hides things.  It's much more effective to measure the time interval between the GPSDO and another local reference.  Of course, you have to have another reference!  You also need to be able to capture the readings and log them to a PC.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 03, 2015, 04:30:06 am
What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.

from what I can tell the adapter board just provides power to the surplus board, and provides rs232 / 1pps / 10mhz / front panel status LEDs. and mounting holes for the spacers to mount the surplus board. the adapter board appears to be a "universal" board for both the huawei and trimble.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 03, 2015, 04:48:54 am
You know, I just don't believe these TI numbers. Perhaps I don't understand what they represent. I hooked up the Lucent GPSDO 10MHz output to my 53131A, which has its own OCXO that has been calibrated to the Lucent.

Now if the Lucent was really drifting by 10 - 50ns per 1 second interval, unless the timer OCXO was drifting in sync (impossible), I would expect to see variation in the 0.1Hz digit. Instead, it is rock solid all the way out to the 0.0001 digit.

I guess maybe I need to sign up for the time-nuts mailing list and ask someone to explain it (or maybe Ed can explain here).

Believe your counter.  The GPSDO is reporting the TI between its PPS and the calculated PPS based on the received signals.  Problem is, the received signal gets distorted by the ionosphere and maybe by multipath.  This creates jitter in the calculated result.  Over a long period, this jitter averages out to zero.  The OCXO's function is to act as a flywheel to filter out the short-term jitter.  The  PPS is then generated from the OCXO.  The 'gotcha' here is that in the RFTG, the averaging appears to degrade the OCXO's performance - or doesn't completely filter out the short-term jitter.

There are a few things that can be checked to ensure that the jitter is minimized.  Like they say, "Location, location, location".  If the GPSDO doesn't have its location figured correctly, this can be a major cause of jitter.  I don't remember if the RFTG has this feature, but some GPSDOs give you the option to set the length of time for the location survey.  Longer is better!  The survey is just as vulnerable to jitter as the PPS.  A longer survey helps average out the jitter.  Give it a day or two - compare the before and after results. 

Note that measuring the output with a frequency counter isn't a very precise measurement because the counter's gate time results in an averaging function that hides things.  It's much more effective to measure the time interval between the GPSDO and another local reference.  Of course, you have to have another reference!  You also need to be able to capture the readings and log them to a PC.

Ed

Thanks, that is a very helpful explanation.

One interesting thing just happened. I was sitting here watching one of robrenz' videos, and all of a sudden the HUP value reset to its starting point (4.32E-4), and the EFC started going nuts. Checking the logs, it looks like it rebooted. After the reboot, it started another survey. I've turned off the survey on boot feature for now. I'm a bit worried as to why it rebooted. It's plugged into a UPS, and I wasn't moving it or doing anything that should have disturbed the (albeit iffy) power connection.

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 03, 2015, 06:10:23 am
I discovered why it rebooted. The UPS is faulty. It's a small Eaton that I bought used, so no surprises there.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 04, 2015, 04:23:22 am
So I think that UPS had been acting up for some time, perhaps very brief cutouts that were enough to disrupt the power supply to the GPSDO. Since removing that from the circuit, the EFC corrections have really settled down, and HUD was as low as 1.1us today  - currently at 1.7us.  The EFC statistics in Z38XX say the EFC slope is 5.025E+01 per day resembling a relative OCXO drift of 5.024E-11 (Hz) per day.
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 04, 2015, 04:49:58 am

What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.

I did a tear down and test of the BG7TBL unit here..

https://drive.google.com/a/skybase.net/file/d/0B9Oysj7clpT7YTBWSjlfNTI1aTQ/view

While I don't have the resolution of KE5FX's test rig ( he has a Cesium standard!) my Thunderbolt based test setup did not show that error.

regards

Tim
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 04, 2015, 05:21:15 am

What is actually on the bg7tbl adapter board - just connectivity to power and the SMA connectors, or is there actually some logic there (i.e. a microcontroller). What I am mainly interested in is if these units are subject to the frequency problem (not exactly 10MHz) that the other BG7TBL design is.

I did a tear down and test of the BG7TBL unit here..

https://drive.google.com/a/skybase.net/file/d/0B9Oysj7clpT7YTBWSjlfNTI1aTQ/view

While I don't have the resolution of KE5FX's test rig ( he has a Cesium standard!) my Thunderbolt based test setup did not show that error.

regards

Tim

Very nice. From which eBay seller did you purchase this unit?
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 04, 2015, 05:38:18 am

Very nice. From which eBay seller did you purchase this unit?

Thanks - I bought from fly-xy, he has a bunch of interesting RF stuff. URL for the GPSDO I bought here...

http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/121530825744 (http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/121530825744)


And here is a newer model with Huawei internals ...

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224)

and yet another model with Trimble internals...

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power/131564496688 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power/131564496688)

regards

Tim
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 04, 2015, 05:56:29 am

Very nice. From which eBay seller did you purchase this unit?

Thanks - I bought from fly-xy, he has a bunch of interesting RF stuff. URL for the GPSDO I bought here...

http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/121530825744 (http://www.ebay.com/itm/10MHZ-OUTPUT-SINE-WAVE-GPS-DISCiPLINED-CLOCK-GPSDO-GPS-Antenna-Power-supply/121530825744)


And here is a newer model with Huawei internals ...

http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224 (http://www.ebay.com/itm/HW-HUAWEI-GPS-DISCIPLINED-CLOCK-GPSDO-OSCILLATOR-Antenna-power-supply-/111716558224)

and yet another model with Trimble internals...

http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power/131564496688 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-Antenna-power/131564496688)

regards

Tim

https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/ (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/)    8)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 04, 2015, 06:07:48 am
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/ (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/)    8)

Excellent idea to collect info on these in one place. Bookmarked.
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 04, 2015, 06:20:07 am
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/ (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/)    8)

Excellent idea to collect info on these in one place. Bookmarked.

!! +1 that  :-+
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 04, 2015, 06:30:51 am
i have a bg7tbl huawei (oscilloquartz star 4), and i'm waiting for delivery of a bg7tbl trimble.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 04, 2015, 06:23:47 pm
i have a bg7tbl huawei (oscilloquartz star 4), and i'm waiting for delivery of a bg7tbl trimble.

Excellent. Looking forward to some comparisons.
Title: Re: Economical option for precision frequency reference?
Post by: EV on August 05, 2015, 11:28:08 am
I'm assuming most of these posts are referring to the

LUCENT/SYMMETRICOM/HP Z3810AS, KS24361 L101 REF0 / L102 REF1, GPSDO TIMING SYSTEM

This REF0 unit has no GPS antenna connector. However it has "NO GPS" led. Can it be used as GPS reference separately without REF1 unit? Are there any instructions or manuals for these?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 05, 2015, 03:00:49 pm
I'm assuming most of these posts are referring to the

LUCENT/SYMMETRICOM/HP Z3810AS, KS24361 L101 REF0 / L102 REF1, GPSDO TIMING SYSTEM

This REF0 unit has no GPS antenna connector. However it has "NO GPS" led. Can it be used as GPS reference separately without REF1 unit? Are there any instructions or manuals for these?

There was some discussion about this on the time-nuts mailing list. There was speculation that an external GPS could be hooked up and providing only the 1PPS signal to REF0, to allow a 21st century GPS chip to work with it and avoid the crappy insensitive chip that's in there now. However, I read every single message on time-nuts about this unit, and no one ever reported back as having even tried this.

AFAIK, there is no manual publicly available for these units. They were created as a drop-in replacement for an earlier unit, the KS-24019, and it is similar to a later unit, the Z3805A, for which I believe there is some documentation.
Title: Re: Economical option for precision frequency reference?
Post by: usagi on August 05, 2015, 10:10:27 pm
There was some discussion about this on the time-nuts mailing list. There was speculation that an external GPS could be hooked up and providing only the 1PPS signal to REF0, to allow a 21st century GPS chip to work with it and avoid the crappy insensitive chip that's in there now. However, I read every single message on time-nuts about this unit, and no one ever reported back as having even tried this.

why bother, just get a bg7tbl oscilloquartz or bg7tbl trimble and be done with it.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 05, 2015, 11:35:14 pm
There was some discussion about this on the time-nuts mailing list. There was speculation that an external GPS could be hooked up and providing only the 1PPS signal to REF0, to allow a 21st century GPS chip to work with it and avoid the crappy insensitive chip that's in there now. However, I read every single message on time-nuts about this unit, and no one ever reported back as having even tried this.

why bother, just get a bg7tbl oscilloquartz or bg7tbl trimble and be done with it.

Yes, I agree. Just answering his question :)
Title: Re: Economical option for precision frequency reference?
Post by: dadler on August 06, 2015, 12:51:14 am
So, I have some information about the RFTG units.

I've shared my personal directory here:

https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0 (https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0)

There is some software and an RFTG user manual from 1996. You guys might already have this stuff, but just thought I'd share just in case.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 06, 2015, 03:22:38 am
I have a rftgm-II at home if anyone wants a teardown.
Title: Re: Economical option for precision frequency reference?
Post by: EV on August 06, 2015, 05:39:33 am
Thanks for the info to motocoder and dadler!
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 06, 2015, 05:49:27 am
So, I have some information about the RFTG units.

I've shared my personal directory here:

https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0 (https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0)

There is some software and an RFTG user manual from 1996. You guys might already have this stuff, but just thought I'd share just in case.

So this is the manual for the older unit that the KS-24361 is patterned on, right?

For anyone thinking of downloading - the software does not run on recent versions of Windows.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 06, 2015, 06:05:13 am
So I posted in the other thread, but forgot to post here that I obtained one of the BG7TBL 2015-07-17 "Trimble" units. This is basically a board NOT designed by BG7TBL, grafted onto a board of his design that provides connectivity to front-panel LEDs, DB9 RS-232 connector, power and RF connectors. My unit is all sealed up in an aluminum box, although I am a bit concerned about it overheating and may pull it out (the box doesn't feel hot at all, so maybe OK). It came with a puck antenna and power supply. Notably the antenna is labelled 3.3V, but the "documentation" that came with this unit clearly says it uses 5V antennas.

If the antenna is placed outside (my "lab" is apparently a GPS dead zone - only the most sensitive of GPS chips will lock up indoors there), it locks up within just a few minutes. The box puts out a very nice and clean sine wave. I don't have the ability to measure phase noise on it, so can't comment about how clean it is. If I hook it up to my scope, and trigger on the signal from the Lucent, I can see a very consistent and repeatable drift in phase between the two references of about 27ns. I need a third unit of some type to see what is responsible for this phase drift.

I will have to fashion an adapter cable to hook up RS-232 and see what can be done with that. The software that came with the unit will not run on my machine; it just errors out looking for some ancient VB6 OCX component (MSCOMM32.OCX).

Pros

Cons
Title: Re: Economical option for precision frequency reference?
Post by: dadler on August 06, 2015, 06:10:30 am
So, I have some information about the RFTG units.

I've shared my personal directory here:

https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0 (https://www.dropbox.com/sh/osgb29wvgnxag4v/AABzYRcHALPExnaa6hU7MLeua?dl=0)

There is some software and an RFTG user manual from 1996. You guys might already have this stuff, but just thought I'd share just in case.

So this is the manual for the older unit that the KS-24361 is patterned on, right?

For anyone thinking of downloading - the software does not run on recent versions of Windows.

Yeah it's an old manual for an ancestor revision, but I was told that most of the communication protocol stuff and other configuration info should be relevant to the newer boxes.

And yeah, I never got the software to work myself but I didn't try that hard. The guy I got the Lucent box from gave it to me--and said he didn't know if it was compatible with the particular Lucent RFTG box or not. I have some more info in paper form, let me "scan" it and upload the PDF.
Title: Re: Economical option for precision frequency reference?
Post by: dadler on August 06, 2015, 06:43:27 am
So I never really looked at the paperwork before, I guess it's not that useful but I scanned it anyways:

https://www.dropbox.com/s/n4nt3yhdt5mc10r/Lucent_RFTGm_II_XO_Notes.pdf?dl=0 (https://www.dropbox.com/s/n4nt3yhdt5mc10r/Lucent_RFTGm_II_XO_Notes.pdf?dl=0)

Keep in mind that the unit I have is the RFTGm-II-XO, which is different than those with the open enclosures. It has a similar front plate, but the entire enclosure is a big, sealed heat sink. However I believe these are all similar architecture devices.

(https://dl.dropboxusercontent.com/s/sqq694cs69io117/RFTGm-II-XO2.jpg)
(https://dl.dropboxusercontent.com/s/96a402ntclbtw7w/RFTGm-II-XO1.jpg)
(https://dl.dropboxusercontent.com/s/pvq8yhccqb809a6/RFTGm-II-XO3.jpg)
Title: Re: Economical option for precision frequency reference?
Post by: EV on August 06, 2015, 07:07:07 am
Cons
  • No usable software
  • ...

Have you tried tboltmon.exe? You can get it here under references:

http://www.prc68.com/I/ThunderBolt.shtml#Tboltmon (http://www.prc68.com/I/ThunderBolt.shtml#Tboltmon)
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 06, 2015, 07:46:27 am

Have you tried tboltmon.exe? You can get it here under references:

http://www.prc68.com/I/ThunderBolt.shtml#Tboltmon (http://www.prc68.com/I/ThunderBolt.shtml#Tboltmon)

That's actually a good idea. Trimble have their own language for their GPSDO's called TSIP. It's the only language Thunderbolts talk. Other Trimble's can be made to talk NMEA but probably only after you've spoken to it in TSIP!

regards

Tim
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 06, 2015, 08:47:49 pm
dadler - thanks for scanning and uploading the docs on the RTFG.

EV and TSL - I will give tboltmon a try. I need to fashion an adapter cable before I can connect it up. Fortunately, the pinout is printed right on the front panel. I have to look up the pinout of the standard PC serial port - it may just need a gender changer (aka "null modem").

(Edit) Looks like a standard USB to serial adapter will work. I'll have to order one from Amazon, though, as all the ones here are USB to Serial/Null-Modem (i.e. a female DB9 connector).
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 06, 2015, 10:57:59 pm
TboltMon isn't the only program that can read TSIP, but it is mostly aimed at Thunderbolt owners. A better piece of software would be Trimble Studio and/or TSIP talker. You can get them from here...

ftp://ftp.trimble.com/pub/sct/embedded/bin/

regards

Tim
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 07, 2015, 05:31:48 am
I discovered that I can hook up Z38XX to either unit's diagnostic port, and see not just the OCXO data but also the GPS data. Given the GPS board is only in the REF1 unit, this MUST mean that there is some sort of communications link between REF0 and REF1 on the J5 interface cable.

I mention this because there was speculation on the time-nuts mailing list that the interface was very simple voltage-level signalling and the 1PPS signal only. That's clearly wrong, as there would be no way for REF0 to know what satellites REF1 was tracking were that the case.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on August 07, 2015, 01:56:51 pm
I discovered that I can hook up Z38XX to either unit's diagnostic port, and see not just the OCXO data but also the GPS data. Given the GPS board is only in the REF1 unit, this MUST mean that there is some sort of communications link between REF0 and REF1 on the J5 interface cable.

I mention this because there was speculation on the time-nuts mailing list that the interface was very simple voltage-level signalling and the 1PPS signal only. That's clearly wrong, as there would be no way for REF0 to know what satellites REF1 was tracking were that the case.

There is a lot happening on J5.

https://www.febo.com/pipermail/time-nuts/2014-November/087970.html (https://www.febo.com/pipermail/time-nuts/2014-November/087970.html)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 07, 2015, 02:24:28 pm
I discovered that I can hook up Z38XX to either unit's diagnostic port, and see not just the OCXO data but also the GPS data. Given the GPS board is only in the REF1 unit, this MUST mean that there is some sort of communications link between REF0 and REF1 on the J5 interface cable.

I mention this because there was speculation on the time-nuts mailing list that the interface was very simple voltage-level signalling and the 1PPS signal only. That's clearly wrong, as there would be no way for REF0 to know what satellites REF1 was tracking were that the case.

There is a lot happening on J5.

https://www.febo.com/pipermail/time-nuts/2014-November/087970.html (https://www.febo.com/pipermail/time-nuts/2014-November/087970.html)

Thanks. There's still a missing piece of the puzzle there, however. As it mentioned in that post, there must be some way that REF0 is able to send commands to the GPS receiver in REF1, possibly proxying through the micro on REF1.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 07, 2015, 06:30:27 pm
I discovered that I can hook up Z38XX to either unit's diagnostic port, and see not just the OCXO data but also the GPS data. Given the GPS board is only in the REF1 unit, this MUST mean that there is some sort of communications link between REF0 and REF1 on the J5 interface cable.

I mention this because there was speculation on the time-nuts mailing list that the interface was very simple voltage-level signalling and the 1PPS signal only. That's clearly wrong, as there would be no way for REF0 to know what satellites REF1 was tracking were that the case.

There is a lot happening on J5.

https://www.febo.com/pipermail/time-nuts/2014-November/087970.html (https://www.febo.com/pipermail/time-nuts/2014-November/087970.html)

Thanks. There's still a missing piece of the puzzle there, however. As it mentioned in that post, there must be some way that REF0 is able to send commands to the GPS receiver in REF1, possibly proxying through the micro on REF1.

There's some current discussion on Time-Nuts on this topic.  Check out the archive:

https://www.febo.com/pipermail/time-nuts/2015-August/093303.html (https://www.febo.com/pipermail/time-nuts/2015-August/093303.html)

This behaviour sounds identical to what I saw with another member of the Z38 family.  The Z3817A was made for Motorola.  It listens to a GPS and can report anything it hears, but it has no ability to control the GPS.  It disciplines its OCXO to the incoming PPS.  It looks like they copied this behaviour for the Lucent units.

The Z3817A happens to be the best GPSDO I've got.  When I measure the PPS output, the standard deviation of the period is < 0.1 ns with a max-min range of < 1 ns.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 07, 2015, 08:13:50 pm
I discovered that I can hook up Z38XX to either unit's diagnostic port, and see not just the OCXO data but also the GPS data. Given the GPS board is only in the REF1 unit, this MUST mean that there is some sort of communications link between REF0 and REF1 on the J5 interface cable.

I mention this because there was speculation on the time-nuts mailing list that the interface was very simple voltage-level signalling and the 1PPS signal only. That's clearly wrong, as there would be no way for REF0 to know what satellites REF1 was tracking were that the case.

There is a lot happening on J5.

https://www.febo.com/pipermail/time-nuts/2014-November/087970.html (https://www.febo.com/pipermail/time-nuts/2014-November/087970.html)

Thanks. There's still a missing piece of the puzzle there, however. As it mentioned in that post, there must be some way that REF0 is able to send commands to the GPS receiver in REF1, possibly proxying through the micro on REF1.

There's some current discussion on Time-Nuts on this topic.  Check out the archive:

https://www.febo.com/pipermail/time-nuts/2015-August/093303.html (https://www.febo.com/pipermail/time-nuts/2015-August/093303.html)

This behaviour sounds identical to what I saw with another member of the Z38 family.  The Z3817A was made for Motorola.  It listens to a GPS and can report anything it hears, but it has no ability to control the GPS.  It disciplines its OCXO to the incoming PPS.  It looks like they copied this behaviour for the Lucent units.

The Z3817A happens to be the best GPSDO I've got.  When I measure the PPS output, the standard deviation of the period is < 0.1 ns with a max-min range of < 1 ns.

Ed

Now that I have two GPSDO - the Lucent and the Trimble - I've been doing some experiments to compare the two. I also have the (Morion) OCXO in my 53131A frequency counter.

If I hook the Lucent to channel one on my scope, and the Trimble to channel two, trigger off channel one and set infinite persistance, I can get some data on how much the relative phases of the two units drift. It has been steadily improving since I plugged the Trimble unit in. Right now there is as much as 17ns drift between the two, which I think is pretty good. I suspect the bulk of this is the Trimble, probably because it has only been plugged in for a few days. I say this because if I hook up the two GPSDO to my frequency counter, using its internal OCXO as the reference, I can see that the Trimble unit has quite a bit more drift than the Lucent. The Lucent drift is < 0.0003 Hz, whereas the Trimble is closer to 0.001 Hz. Obviously the OCXO in my counter is also not perfect, but I think as a relative measurement this is a valid technique for a rough comparison of the two GPSDO.

Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 07, 2015, 10:30:32 pm

The Z3817A happens to be the best GPSDO I've got.  When I measure the PPS output, the standard deviation of the period is < 0.1 ns with a max-min range of < 1 ns.

Ed

OK... how were you measuring that ? What's your base reference ?

thanks

Tim
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 07, 2015, 10:43:32 pm

The Z3817A happens to be the best GPSDO I've got.  When I measure the PPS output, the standard deviation of the period is < 0.1 ns with a max-min range of < 1 ns.

Ed

OK... how were you measuring that ? What's your base reference ?

thanks

Tim

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.  I made multiple runs of ~1000 readings per run.  Notice that I didn't say what the period was, only what the standard deviation was.  The 5370B reports that directly.  That means the absolute accuracy isn't relevant, just the resolution.  This test measures jitter.  The assumption with any GPSDO is that they've got the basics right and the frequency is correct.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 12:15:29 am
TboltMon isn't the only program that can read TSIP, but it is mostly aimed at Thunderbolt owners. A better piece of software would be Trimble Studio and/or TSIP talker. You can get them from here...

ftp://ftp.trimble.com/pub/sct/embedded/bin/

regards

Tim

Ok, TrimbleStudio does not appear to work with this device, despite it being labelled as "Trimble". The docs mention a protocol called UCCM. If I connect to the device with a serial terminal, at 57600/8/N/1, I get a UCCM-P prompt, and if I type help it lists the commands below. This appears similar, but not identical to the Lucent command set. For example, you do not enter a ":" character before running a command like "SYST:STAT?". Entering that command gives the following response (GPS coordinates removed):

UCCM-P >SYSTEM:STATUS?

-------------------------------------------------------------------------------
57964-80     serial number  60498671     firmware ver  2.0.1.6-01 LINK    mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
XX Ref 8KHz 0: [LOS]
XX Ref 8KHz 1: [LOS]                          TFOM     2            FFOM      0
XX Ref 8KHz 2: [LOS]                          UCCM A Status[ACTIVE]
XX Ref 8KHz 3: [LOS]
>> GPS: [phase:-8.6E-08]
ACQUISITION ...................................................[GPS 1PPS Valid]
Tracking: 5 ____   Not Tracking: 6 ________   Time ____________________________
PRN  El  Az  C/N   PRN  El  Az                GPS      00:13:33     08 Aug 2015
  2  14  73   35     5  45  62
 26  31 307   33    25  31 195                ANT DLY  10 ns
 29  85  88   47    16  10 327                Position ________________________
 20  61 162   43    18  10 205                MODE     Hold
 13  11 108   36    15   7 141
                    21  44 261                LAT      N  xx:xx:xx.xxx
                                              LON      W xxx:xx:x.xxx
                                              HGT              +xxx.xx m (MSL)



Commands
*IDN?
ALARm:HARDware?
ALARm:OPERation?
DIAGnostic:OUTPut ON|OFF
OUTPut:REFerence?
OUTPut:ACTive:ENABle
OUTPut:ACTive:DISable
OUTPut:ACTive:HOLDover:DURation:THReshold <seconds>
OUTPut:ACTive:HOLDover:DURation:THReshold?
OUTPut:INACTive
OUTPut:INACTive?
OUTPut:STATe?
SYNChronization:HOLDover:DURation:STATus:THReshold <seconds>
SYSTem:PRESet
SYNChronization:TFOMerit?
LED:GPSLock?
SYNChronization:FFOMerit?
GPS:POSition N or S,<deg>,<min>,<sec>,E or W,<deg>,<min>,<sec>,<height>
GPS:POSition?
GPS:POSition:HOLD:LAST?
GPS:REFerence:ADELay <numeric value>
GPS:REFerence:ADELay?
GPS:SATellite:TRACking:COUNt?
GPS:SATellite:TRACking?
DIAGnostic:ROSCillator:EFControl:RELative?
SYNChronization:TINTerval?
DIAGnostic:LOG:READ:ALL?
DIAGnostic:LOG:CLEar
SYSTem:PON
OUTPut:MODE?
SYSTem:STATus?
SYSTem:COMMunication:SERial1:BAUD 9600|19200|38400|57600
SYSTem:COMMunication:SERial1:BAUD?
SYSTem:COMMunication:SERial1:PRESet
SYSTem:COMMunication:SERial2:BAUD 9600|19200|38400|57600
SYSTem:COMMunication:SERial2:BAUD?
SYSTem:COMMunication:SERial2:PRESet
OUTPut:STANby:THReshold <seconds>
changeSN
SYNChronization:REFerence:ENABLE LINK|GPS
SYNChronization:REFerence:DISABLE LINK|GPS
SYNChronization:REFerence:ENABLE?
STATus
POSSTATus
TOD EN|DI
TIME:STRing?
REFerence:TYPE GPS|LINK
REFerence:TYPE?
PULLINRANGE 0|1|2|...|254|255
PULLINRNAGE?
DIAGnostic:LOOP?
DIAGnostic:ROSCillator:EFControl:DATA GPS|<value>
DIAGnostic:ROSCillator:EFControl:DATA?
OUTut:TP:SELection PP1S|PP2S
OUTut:TP:SELection?
GPSystem:SATellite:TRACking:EMANgle <degrees>
GPSystem:SATellite:TRACking:EMANgle?
DIAGnostic:TCODe:STATus:AMASk
DIAGnostic:TCODe:STATus:OMASk
DIAGnostic:TCODe:ERRor:AMASk
DIAGnostic:TCODe:ERRor:OMASk
DIAGnostic:HOLDover:DELay
DIAGnostic:HOLDover:DELay?
GPS:SATellite:TRACking:IGNore <PRN>, ...,<PRN>
GPS:SATellite:TRACking:IGNore?
GPS:SATellite:TRACking:INCLude <PRN>, ...,<PRN>
GPS:SATellite:TRACking:INCLude?
GPS:SATellite:TRACking:<select>:ALL
? or HELP

Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 08, 2015, 12:53:32 am

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.


Very nice, wish I had one of those in my lab :)


Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 08, 2015, 01:21:26 am


Commands
*IDN?


This is SCPI the *IDN? is a dead giveaway!

http://www.ivifoundation.org/scpi/default.aspx (http://www.ivifoundation.org/scpi/default.aspx)

http://www.ivifoundation.org/docs/scpi-99.pdf (http://www.ivifoundation.org/docs/scpi-99.pdf)

Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 01:40:59 am

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.


Very nice, wish I had one of those in my lab :)

Actually, that's not my best time interval measurement tool.

https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391 (https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391)

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 01:55:08 am


Commands
*IDN?


This is SCPI the *IDN? is a dead giveaway!

http://www.ivifoundation.org/scpi/default.aspx (http://www.ivifoundation.org/scpi/default.aspx)

http://www.ivifoundation.org/docs/scpi-99.pdf (http://www.ivifoundation.org/docs/scpi-99.pdf)

Nope, it's someone's half-ass copy of SCPI. If it was SCPI, you'd commands with either a ':' or a "*".

I think this thing can return all the same sort of useful information you can get with the other units, but it just seems to be some proprietary command set that isn't going to be compatible with any software out there. That's really ashame, as it otherwise seems like a decent unit. Many of the commands are the same, but without the ':" prefix on them, the software isn't going to work.
Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 08, 2015, 02:08:06 am

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.


Very nice, wish I had one of those in my lab :)

Actually, that's not my best time interval measurement tool.

https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391 (https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391)

Ed


Cricky - that's nice too :-+ and a quick search shows the 2079's selling for reasonable $ - ggrrr too many toys, not enough budget ! :)



Title: Re: Economical option for precision frequency reference?
Post by: TSL on August 08, 2015, 02:12:15 am

Nope, it's someone's half-ass copy of SCPI. If it was SCPI, you'd commands with either a ':' or a "*".

I think this thing can return all the same sort of useful information you can get with the other units, but it just seems to be some proprietary command set that isn't going to be compatible with any software out there. That's really ashame, as it otherwise seems like a decent unit. Many of the commands are the same, but without the ':" prefix on them, the software isn't going to work.

You're right! - I should have looked closer, didn't even notice the : was missing.

And that's bloody annoying -  :wtf: why only go 99% of the way ?
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 08, 2015, 03:16:20 am

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.


Very nice, wish I had one of those in my lab :)
I assume that you figured out how to use it, can you show us what it does.

Actually, that's not my best time interval measurement tool.

https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391 (https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391)

Ed
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 07:28:22 am

I was using an HP 5370B (resolution of < 50 ps - yes picoseconds) referenced to my Efratom FRT Rb standard.


Very nice, wish I had one of those in my lab :)


Actually, that's not my best time interval measurement tool.

https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391 (https://www.eevblog.com/forum/testgear/wavecrest-dts-2077-teardown/msg279391/#msg279391)

Ed
I assume that you figured out how to use it, can you show us what it does.

It's a Time Interval Counter.  It measures frequency, time from A to B, rise time, fall time, period, pulse width, etc.  But it does it *really* well!  :)  I've been struggling to extract its full potential because it needs an input with very sharp rise and fall times.  Forget 10 MHz, even 100 MHz isn't really enough, 1 GHz is okay!  I built a circuit to square up a 5 or 10 MHz signal so that it can be properly measured, but it needs a little more work.

One of the particularly neat features is called a "strobing voltmeter".  It allows you to sample the input at time intervals as small as 10 ps and report the results.  In other words, it's digitizing the signal at 100 Gs/s.   :o  I threw together a proof-of-concept program to test this.  The attached picture is the output from my squaring circuit.  Due to limitations in the strobing voltmeter, it took me quite a while to figure out how to get this picture.  Initially I didn't think I would be able to do it.  The horizontal scale is in units of 100 ps.  The vertical scale is in volts.  The voltage is small because the maximum voltage on the input is only 1.7 volts.  I really don't want to blow the input on this thing!

Ed

Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 08, 2015, 08:13:06 am
So for the display, what can you get out if it(resolution/digits). Yes, i read the manual, i replied in your orig thread.
Title: Re: Economical option for precision frequency reference?
Post by: bingo600 on August 08, 2015, 09:57:17 am

One of the particularly neat features is called a "strobing voltmeter".  It allows you to sample the input at time intervals as small as 10 ps and report the results.  In other words, it's digitizing the signal at 100 Gs/s.   :o  I threw together a proof-of-concept program to test this.  The attached picture is the output from my squaring circuit.  Due to limitations in the strobing voltmeter, it took me quite a while to figure out how to get this picture.  Initially I didn't think I would be able to do it.  The horizontal scale is in units of 100 ps.  The vertical scale is in volts.  The voltage is small because the maximum voltage on the input is only 1.7 volts.  I really don't want to blow the input on this thing!

Ed

Hi Ed

I have a 2079 , any chance of a copy of your proof program ?
The strobo graph seems really usefull

/Bingo
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 05:12:49 pm
So for the display, what can you get out if it(resolution/digits). Yes, i read the manual, i replied in your orig thread.

I just measured a time interval from A to B.  The reported result was 753,191,898.407 ps as the average of 1000 results.  It also displays Std. Dev. (113.2 ps) and pk (+- 199.9 ps).  The measurement took a couple of seconds because the input frequency was only 500 Hz.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 05:35:47 pm
Hi Ed

I have a 2079 , any chance of a copy of your proof program ?
The strobo graph seems really usefull

/Bingo

Sent via PM
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 06:10:45 pm
Some more info on the Trimble/Wun-Hung-Lo hybrid. I powered it down to drill some ventilation holes in the case. Upon powering it back up, I see that the elevation mask setting has been reset.

So apparently they don't write settings to non-volatile RAM.  :-DD
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 06:37:48 pm
Some more info on the Trimble/Wun-Hung-Lo hybrid. I powered it down to drill some ventilation holes in the case. Upon powering it back up, I see that the elevation mask setting has been reset.

So apparently they don't write settings to non-volatile RAM.  :-DD

Maybe there is no non-volatile RAM in these units.  It appears that they came from a telco environment where they would be powered off of continuously float-charged lead-acid batteries.  They would never be powered down so, no need for non-volatile storage.  With a bit of reverse-engineering you should be able to add a battery backup to the GPS receiver itself.  It's designed to support that.

FYI, I have a similar Trimble GPSDO that I obtained from a source other than our favorite auction site.  It's command prompt is UCCM> rather than UCCM-P>.  The OCXO is a Trimble 65256 with a 2006 date code instead of a 73090 unit with 2009 or 2010 date code.  The performance seems similar to the RFTG.  In other words, not as good as the Trimble Thunderbolt or other members of the Z38 family.  I unsoldered the OCXO and found that, by itself, the performance (other than aging) is better than when it's in the circuit.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 06:48:11 pm
Some more info on the Trimble/Wun-Hung-Lo hybrid. I powered it down to drill some ventilation holes in the case. Upon powering it back up, I see that the elevation mask setting has been reset.

So apparently they don't write settings to non-volatile RAM.  :-DD

Maybe there is no non-volatile RAM in these units.  It appears that they came from a telco environment where they would be powered off of continuously float-charged lead-acid batteries.  They would never be powered down so, no need for non-volatile storage.  With a bit of reverse-engineering you should be able to add a battery backup to the GPS receiver itself.  It's designed to support that.

FYI, I have a similar Trimble GPSDO that I obtained from a source other than our favorite auction site.  It's command prompt is UCCM> rather than UCCM-P>.  The OCXO is a Trimble 65256 with a 2006 date code instead of a 73090 unit with 2009 or 2010 date code.  The performance seems similar to the RFTG.  In other words, not as good as the Trimble Thunderbolt or other members of the Z38 family.  I unsoldered the OCXO and found that, by itself, the performance (other than aging) is better than when it's in the circuit.

Ed

Well, it does provide a command to set the serial number, and if you set that, it does persist past a power cycle. So there must be some non-volatile storage there.

And even if their wasn't, that's shoddy design IMHO. Even if you expect it to be battery backed up indefinitely, if you ever have to do maintenance on the equipment, or if there is some AOG that removes power for an extended period of time, when the power is restored your technician will need to re-configure everything. It's hard to find a microcontroller these days without some built-in EEPROM, so I think most engineers would back up the settings in EEPROM.

But drawing some conclusions from the firmware and the non-functional software they provided with this unit, I think this is classic Wun-Hung-Lo engineering, so I am not surprised that they didn't bother to add the few extra lines of code to store the GPS settings in non-volatile RAM and restore them on power-up.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 06:50:49 pm
By the way, Ed - the Lucent seems to be almost an order of magnitude more stable than this thing so far. It's interesting to watch the Lucent OCXO age. The EFC voltage has been following a general upward trend since I powered it on. I guess at some point, this will level off, and at that point the OCXO will be considered broken in?
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on August 08, 2015, 07:39:21 pm
By the way, Ed - the Lucent seems to be almost an order of magnitude more stable than this thing so far. It's interesting to watch the Lucent OCXO age. The EFC voltage has been following a general upward trend since I powered it on. I guess at some point, this will level off, and at that point the OCXO will be considered broken in?

Not really.  OCXOs age - period.  That's why you need a GPSDO - to lock the OCXO to a stable reference and keep the frequency constant.  What will happen is that the rate of aging will slow down to the specified value for the OCXO or lower.  If you had 100 OCXOs of the same type you'd find that aging could be high or low, positive or negative depending on the individual unit.  Aging could be positive one day and negative the next, even after you've accounted for changes in temperature, supply voltage, humidity (yes!), air pressure (yes!) etc.  Whether the levels are significant depends on the user and the application.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 08, 2015, 07:44:03 pm
By the way, Ed - the Lucent seems to be almost an order of magnitude more stable than this thing so far. It's interesting to watch the Lucent OCXO age. The EFC voltage has been following a general upward trend since I powered it on. I guess at some point, this will level off, and at that point the OCXO will be considered broken in?

Not really.  OCXOs age - period.  That's why you need a GPSDO - to lock the OCXO to a stable reference and keep the frequency constant.  What will happen is that the rate of aging will slow down to the specified value for the OCXO or lower.  If you had 100 OCXOs of the same type you'd find that aging could be high or low, positive or negative depending on the individual unit.  Aging could be positive one day and negative the next, even after you've accounted for changes in temperature, supply voltage, humidity (yes!), air pressure (yes!) etc.  Whether the levels are significant depends on the user and the application.

Ed

I see. Well, the PPS excursions reported by Z38XX have definitely settle down since initial power-on. Now it is maybe  50% of the time within +/-10ns, 70% of the time within +/-20 ns, and it does not ever seem to go above about 60ns, whereas when it was first powered on, it was bouncing between +/- 90ns pretty much constantly.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 09, 2015, 05:31:50 am
For those who have the rftg-ii-rb, what is the power input pin.
Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 09, 2015, 05:33:53 am
I bought the Lucent set and it arrived yesterday.  I added a Garmin external antenna and powered the units using a laptop 19.5v brick until I build a better supply.  They came up in about 15 minutes and after locating the antenna optimally I am getting 6 and sometimes 7 satellites.  I thought they only tracked 5 at a time? Satstat works well and the unit finished the survey.  Tfom  and ffom are as low as they go.  Overall very pleased with how smoothly it all went.

I bought them to sync my counters and spectrum analyzer.  The killer is they were hardly off much at all after all that. 

Jerry
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 09, 2015, 06:14:28 am
I bought the Lucent set and it arrived yesterday.  I added a Garmin external antenna and powered the units using a laptop 19.5v brick until I build a better supply.  They came up in about 15 minutes and after locating the antenna optimally I am getting 6 and sometimes 7 satellites.  I thought they only tracked 5 at a time? Satstat works well and the unit finished the survey.  Tfom  and ffom are as low as they go.  Overall very pleased with how smoothly it all went.

I bought them to sync my counters and spectrum analyzer.  The killer is they were hardly off much at all after all that. 

Jerry

They can sync up to 8 satellites at a time.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 09, 2015, 12:01:09 pm
I bought the Lucent set and it arrived yesterday.  I added a Garmin external antenna and powered the units using a laptop 19.5v brick until I build a better supply.  They came up in about 15 minutes and after locating the antenna optimally I am getting 6 and sometimes 7 satellites.  I thought they only tracked 5 at a time? Satstat works well and the unit finished the survey.  Tfom  and ffom are as low as they go.  Overall very pleased with how smoothly it all went.

I bought them to sync my counters and spectrum analyzer.  The killer is they were hardly off much at all after all that. 

Jerry

I am very happy with mine as well. It is more than accurate enough to calibrate my frequency counter.
Title: Re: Economical option for precision frequency reference?
Post by: smgvbest on August 09, 2015, 09:24:15 pm
For those who have the rftg-ii-rb, what is the power input pin.

Pin 1 is +24VDC and Pin 2 is GND
Title: Re: Economical option for precision frequency reference?
Post by: smgvbest on August 09, 2015, 10:21:19 pm
Has anyone used the RTFG.exe on WinXP to configure the RFTGm-II-Rb/RFTGm-II-XO pair?
From the look of it, it was written for Win95 or Windows 3.11.   I can load up an old PC with Win95 if I have to but if anyones gotten it to work on WinXP that would be great to know.

Just mainly looking to program in my cable length or atleast read out what it is.   I've used a FTDI based RS422 interface and can see binary data coming across in teraterm but the RTFG program doesn't seem to connect

I do know using the output of the XO GPD Locked and used on my HP53131A's external ref and then measuring the Rb output I have 10Mhz +/- 200ns
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 09, 2015, 10:59:09 pm
I got it powered, using the db15 connector.
Unless i've messed up, do not try connecting the external comms connectors(rs422) to the db9 on the data/power connector unit.
sparks will fly.
Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 09, 2015, 11:04:18 pm
Today around noon I tripped the breaker powering my ref-0/ref-1 pair.  Prior to this happening my ref-0 was active and transmitting the 15Mhz signal. Ref-1 was in standby. Upon powering the units back up, ref-0 is showing a fault (after the blinking light test) and now ref-1 is active. Ref-0 is remaining in fault state.  Ref-1 is running the survey again.

I looked in the error log and around the time of the failure a "15Mhz output failure" was logged.  Stupid me I cleared the log so I can't read the correct error text.  So I guess what happened is that the ref-0 (which was active) saw the power failure first?  transferred to ref-1?  and now ref-1 will be active until the next failure?  I power cycled them right after the failure so they came up at the same time.  I would have thought ref-0 would have taken over again.  And if ref-1 is active I would have thought ref-0 would be in standby, not fault, no?

Is there a way thru Satstat to have them switch back or is there another way to test the fail-over?  Also, Since the 10Mhz output is on ref-0, does that remain sync'ed when ref-1 is active?

Lastly, I see there is a power-on setting to either have it rerun the survey or use the last known position.  I don't see a way to set it.  Querying the device shows it defaults to rerun.

thanks
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 10, 2015, 02:21:44 am
Today around noon I tripped the breaker powering my ref-0/ref-1 pair.  Prior to this happening my ref-0 was active and transmitting the 15Mhz signal. Ref-1 was in standby. Upon powering the units back up, ref-0 is showing a fault (after the blinking light test) and now ref-1 is active. Ref-0 is remaining in fault state.  Ref-1 is running the survey again.

I looked in the error log and around the time of the failure a "15Mhz output failure" was logged.  Stupid me I cleared the log so I can't read the correct error text.  So I guess what happened is that the ref-0 (which was active) saw the power failure first?  transferred to ref-1?  and now ref-1 will be active until the next failure?  I power cycled them right after the failure so they came up at the same time.  I would have thought ref-0 would have taken over again.  And if ref-1 is active I would have thought ref-0 would be in standby, not fault, no?

Is there a way thru Satstat to have them switch back or is there another way to test the fail-over?  Also, Since the 10Mhz output is on ref-0, does that remain sync'ed when ref-1 is active?

Lastly, I see there is a power-on setting to either have it rerun the survey or use the last known position.  I don't see a way to set it.  Querying the device shows it defaults to rerun.

thanks

I don't think any special command is required for it to switch back. For sure it should go back to REF-0 after power cycle. Double-check your interface cable (J5) and really make sure it's screwed in tight. I saw several reports of people having issues with that cable caused by some of the pins being shorter than normal.
Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 10, 2015, 02:32:36 am
Wrt my lengthy post above, the fault light on ref-0 never went out.  Ref-1 worked as expected and ref-0 continued to output 10Mhz but not the 15Mhz which continued to be supplied by ref-1.  The 'on' light was lit on ref-1;  ref-0 posted a fault light.

For the heck of it, I pulled the power on ref-1.  The 'no gps' light was lit on ref-0 which continued to display 'fault'.  I would have expected ref-0 to go into hold over and output the 15Mhz, but it didn't.  It seems like it outputs 10Mhz all the time. 

I then power cycled both units. After going thru the blink test, the 'on' light on ref-0 lit and it started to output 15Mhz.  I would have expected it to do this when I pulled the power on ref-1 forcing a fail over, but it didn't.  Also, I had changed the power on default to use the last position so it wasn't doing a survey again.

After about 10 minutes of ref-0 outputting 15Mhz with the 'on' and 'fault' lights lit (prior to full gps lock), ref-0 posted errors in the log:
15Mhz Failure Set
Failed Mode Entered
At that point, ref-1 lit its 'on' light and started outputting 15Mhz.  So I guess ref-0 saw a failure and it failed over to ref-1.

I then cycled the power again.  The errors are still in the log, but ref-0 is now doing a survey and acting OK.  Both units have the 'no gps' and 'fault' lights lit (prior to the survey which is normal) with ref-0 also having the 'on' light lit and outputting 15Mhz.

So if you can follow the confusing sequence above, the questions are:

1) If you pull the power on the active unit ('on' light lit), shouldn't it transfer to the other?  If the unit you pull power from is ref-1 with the gps, it should go into hold-over;  if you pull ref-0 (without gps) shouldn't ref-1 just take over and not go into hold over?  You would lose the 10Mhz from ref-0, of course.

2) Based on the sequence above, I suspect my ref-0 which is posting the '15Mhz failure set' errors to have a problem.  It transferred twice to the ref-1 unit.  At first I thought it was because of the power failure but now I suspect not.

3) Does anybody know how it monitors the 15Mhz output to be able to tell when it has a failure?

4) It seems like the 10Mhz is always running.  Is this gps locked?  If so, I would not expect to see it if the gps wasn't up.

5) Under normal operation, what lights are lit on your units?  Which of the two is the default for 15Mhz?   I thought when my set were working correctly, ref-1 was in standby and ref-0 had the 'on' light lit and was outputting both 10Mhz and 15Mhz.

I am using 19.6V to drive both of them.  I had seen posted that the DC-DC converter takes anything from 18 to like 36V.  I plan to build a better power supply but I am starting to think maybe I am too close to the 18V.

Sorry for the long confusing posts.

Jerry
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on August 10, 2015, 03:26:29 am
I had the same issue earlier today in which the xo stayed offline, while the rb remained online. Similiar to your a bad piwer connection caused the xo to lose power while the. Rb stayed online. A power cycle fixed that.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 10, 2015, 03:33:52 am
I am using 19.6V to drive both of them.  I had seen posted that the DC-DC converter takes anything from 18 to like 36V.  I plan to build a better power supply but I am starting to think maybe I am too close to the 18V.

19.6V is fine, but the lower the input voltage, the more amperage is required. There are some LEDs near rear left of the unit (looking down from above), just to the right of the DC-DC converter. If power is OK, you should see one green LED blinking at a rate of about once per second. If you see anything else, there is a power fault. Can you check this, especially during start-up sequencing (it draws more power during that phase)?
Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 10, 2015, 04:10:19 am
Moto, the internal power lights are fine as you stated, slowly blinking green.

I came down after dinner where before I had recycled the power.  Ref-0 (where I had the fault) was now ok, no fault, and 'on' putting out 15Mhz;  ref-1 was in 'standby' mode.  So it looks like a couple of power cycles plus some  waiting time fixed it.

So not being able to leave well enough alone, I switched the front panel Output level from 17 - 23 on ref-0.  The 'on' lights started blinking in both units and they logged an error that the setting were different.  Ref-0 then failed over to ref-1.  So I set them both back to the same 17 level setting.  I then recycled the units and ref-0, the one I've been having trouble with, is now showing fault again and ref-1 is in 'on' mode.  It posted another 15Mhz failure.

I'm wondering if you have to have the 15Mhz unloaded when it boots?  I'll attempt that next as I try to clear the fault on ref-0.  It might just clear itself.  It shows that it is GPS locked which usually is what clears the fault.

I don't know if I am adding to the wealth of knowledge on these boxes or confusing the subject...

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on August 10, 2015, 04:36:01 am
Moto, the internal power lights are fine as you stated, slowly blinking green.

I came down after dinner where before I had recycled the power.  Ref-0 (where I had the fault) was now ok, no fault, and 'on' putting out 15Mhz;  ref-1 was in 'standby' mode.  So it looks like a couple of power cycles plus some  waiting time fixed it.

So not being able to leave well enough alone, I switched the front panel Output level from 17 - 23 on ref-0.  The 'on' lights started blinking in both units and they logged an error that the setting were different.  Ref-0 then failed over to ref-1.  So I set them both back to the same 17 level setting.  I then recycled the units and ref-0, the one I've been having trouble with, is now showing fault again and ref-1 is in 'on' mode.  It posted another 15Mhz failure.

I'm wondering if you have to have the 15Mhz unloaded when it boots?  I'll attempt that next as I try to clear the fault on ref-0.  It might just clear itself.  It shows that it is GPS locked which usually is what clears the fault.

I don't know if I am adding to the wealth of knowledge on these boxes or confusing the subject...

The output level alarm is well-known. One of the pins on J5 indicates the level setting. How long have you waited to see if the fault clears? I'd wait at least 10 minutes to see if things return to a normal state.

Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 10, 2015, 06:13:23 am
I power cycled them again and all is back to normal.  If I had to point to anything I would think the problem is inconsistent application of power.  We'll see if the 15Mhz failure comes back.

Thanks for the pointers.

Jerry

btw:  when ref-0 faulted with the 15Mhz error, I waited about an hour for it to clear without luck.   The good news was it failed-over.  I'd still like to know what the 15Mhz error means and how they track it. 
Title: Re: Economical option for precision frequency reference?
Post by: cncjerry on August 11, 2015, 12:56:55 am
Once the survey is complete and the units have been running for a while, how many sats does it have to lock to maintain its best sync?  I can get 4 sat reliably with my antenna outside my shop;  If put it on my railing three stories up I can get 8.  Just wondering if 4 sats are enough for long term operation.

thanks

Jerry
Title: Re: Economical option for precision frequency reference?
Post by: Dragon88 on August 18, 2015, 04:35:01 am
Jerry,

I'll try to answer some of your questions. I've been working on these units quite a bit the past couple weeks, with the goal of getting the two boxes (REF-0 and REF-1) to operate independently of each other. I have been successful in this, and have learned a lot about them in the process.

- Each unit knows the status of the other unit using pins on the interface connector. There is no sophisticated signaling. The logic level of three pins in particular tell the REF-0 to initially turn its outputs on. Either by command or through a fault, the REF-1 can take over and turn its own outputs on. I do not know what your own fault is, but I would recommend removing and re-seating the interface cable several times. There may be corrosion on one of the pins which is causing an intermittent connection.

- The 10MHz output on the REF-0 is a test point, and is not a primary output. It is disciplined in that it is generated from the 5MHz OCXO in the unit, which is disciplined to GPS. However, it's status (on or off) is not controlled like the 15MHz primary output is. It's actually buffered by the same chip that generates the clock signal for the processor. A "test point", nothing more. The signal is quite "dirty" compared to the 15MHz output.

- The REF-0 send no commands at all to the GPS. In fact the serial Tx pin from the REF-0 isn't even connected. The REF-0 monitors the GPS strings (and PPS signal) sent from the Oncore GPS to the REF-1, and looks for key fields to know that the GPS lock is good. If it detects that GPS status is degraded, it will enter holdover mode, and recover on its own when the lock is good again. The REF-1 does not guide this process. All the two boxes exchange between each other is "I'm ok and my outputs are on" or "I'm not ok you turn your outputs on". Again, this is merely done with pins on the interface connector for reliability.

- You should always achieve the best antenna position possible.

If you need any more help with your unit, please PM me.  :-+

Dan
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on August 18, 2015, 01:51:21 pm
That's great.

So if you have the information about "which" pins, and a truth table for them, it would be helpful to many people to post the information here.

Thanks!
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on August 19, 2015, 07:08:57 pm
Bought an NTBW50AA from the 'bay the other day, looking forward to firing it up when it arrives. I have read there is a divide by two on the 9.8304 MHz which I plan to remove if possible to output 19.6608 MHz which my Agilent spectrum analyzer can use. It can also use the even second output which should be fun to try. Seemed to be the cheapest option overall that I could find.
Title: Re: Economical option for precision frequency reference?
Post by: artag on August 24, 2015, 01:44:39 am

I'll try to answer some of your questions. I've been working on these units quite a bit the past couple weeks, with the goal of getting the two boxes (REF-0 and REF-1) to operate independently of each other. I have been successful in this, and have learned a lot about them in the process.


Thank you for publishing this work (and thanks to the other time-nuts people who have provided information). I wanted to get one of these going but the low price is rather spoilt by the postage to the UK - about 3 times the price of the units iirc !

The more you ship the cheaper it is .. though bulk does tend to make sure the customs and excise people notice it. Despite that,  I've bought several to make it worthwhile and am just about to take delivery - so if you're in the UK or nearby and want to share in the oscillatory goodness at a CMOT price, get in touch.
 
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 03, 2015, 06:06:51 pm
I recently needed to buy a GPS antenna for my gpsdo and after touring ebay found item 181420921843.
I received it yesterday and can highly recommend it for anyone looking to get a very nice outdoor GPS antenna for a good price.
The listing isn't too great but what you are really getting is a new waterproof Trimble 5 volt 26 db gain antenna, part # 28367-70 and a 5 meter RG316 cable made by Huber Suhner with a TNC on one end for the antenna and an SMA on the other. The cable is very highly quality - no cheap chinese parts.
Pretty tough to beat this combo for 15.99 USD shipped for those in the US.

I have no affiliation with the seller, just like a good deal and this kit is ideal for many gpsdo owners.

edit - aww, they just put the price back to 19.99 for them, still a good deal but not as good.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 03, 2015, 07:34:55 pm
I recently needed to buy a GPS antenna for my gpsdo and after touring ebay found item 181420921843.
I received it yesterday and can highly recommend it for anyone looking to get a very nice outdoor GPS antenna for a good price.
The listing isn't too great but what you are really getting is a new waterproof Trimble 5 volt 26 db gain antenna, part # 28367-70 and a 5 meter RG316 cable made by Huber Suhner with a TNC on one end for the antenna and an SMA on the other. The cable is very highly quality - no cheap chinese parts.
Pretty tough to beat this combo for 15.99 USD shipped for those in the US.

I have no affiliation with the seller, just like a good deal and this kit is ideal for many gpsdo owners.

edit - aww, they just put the price back to 19.99 for them, still a good deal but not as good.

The antenna is waterproof, but what about the connector? On the Symmetricon antenna that I have, the connection is made inside a tube, the top of which is sealed with a gasket. So unless you mount it upside down, water can't get in. As you say the listing isn't too good, but based on the picture that's there it looks like water could get into the connector.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 03, 2015, 08:01:16 pm
I recently needed to buy a GPS antenna for my gpsdo and after touring ebay found item 181420921843.
I received it yesterday and can highly recommend it for anyone looking to get a very nice outdoor GPS antenna for a good price.
The listing isn't too great but what you are really getting is a new waterproof Trimble 5 volt 26 db gain antenna, part # 28367-70 and a 5 meter RG316 cable made by Huber Suhner with a TNC on one end for the antenna and an SMA on the other. The cable is very highly quality - no cheap chinese parts.
Pretty tough to beat this combo for 15.99 USD shipped for those in the US.

I have no affiliation with the seller, just like a good deal and this kit is ideal for many gpsdo owners.

edit - aww, they just put the price back to 19.99 for them, still a good deal but not as good.

The antenna is waterproof, but what about the connector? On the Symmetricon antenna that I have, the connection is made inside a tube, the top of which is sealed with a gasket. So unless you mount it upside down, water can't get in. As you say the listing isn't too good, but based on the picture that's there it looks like water could get into the connector.

I'd recommend any outdoor antenna connection be properly sealed in vulcanizing/Self-amalgamating tape.
Title: Re: Economical option for precision frequency reference?
Post by: DimitriP on September 04, 2015, 01:31:39 am
I recently needed to buy a GPS antenna for my gpsdo and after touring ebay found item 181420921843.
I received it yesterday and can highly recommend it for anyone looking to get a very nice outdoor GPS antenna for a good price.
The listing isn't too great but what you are really getting is a new waterproof Trimble 5 volt 26 db gain antenna, part # 28367-70 and a 5 meter RG316 cable made by Huber Suhner with a TNC on one end for the antenna and an SMA on the other. The cable is very highly quality - no cheap chinese parts.
Pretty tough to beat this combo for 15.99 USD shipped for those in the US.

I have no affiliation with the seller, just like a good deal and this kit is ideal for many gpsdo owners.

edit - aww, they just put the price back to 19.99 for them, still a good deal but not as good.

The antenna is waterproof, but what about the connector? On the Symmetricon antenna that I have, the connection is made inside a tube, the top of which is sealed with a gasket. So unless you mount it upside down, water can't get in. As you say the listing isn't too good, but based on the picture that's there it looks like water could get into the connector.

I'd recommend any outdoor antenna connection be properly sealed in vulcanizing/Self-amalgamating tape.

Well crap, now the price of vulcanizing/Self-amalgamating tape will go up too....
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 04, 2015, 02:54:10 am
I recently needed to buy a GPS antenna for my gpsdo and after touring ebay found item 181420921843.
I received it yesterday and can highly recommend it for anyone looking to get a very nice outdoor GPS antenna for a good price.
The listing isn't too great but what you are really getting is a new waterproof Trimble 5 volt 26 db gain antenna, part # 28367-70 and a 5 meter RG316 cable made by Huber Suhner with a TNC on one end for the antenna and an SMA on the other. The cable is very highly quality - no cheap chinese parts.
Pretty tough to beat this combo for 15.99 USD shipped for those in the US.

I have no affiliation with the seller, just like a good deal and this kit is ideal for many gpsdo owners.

edit - aww, they just put the price back to 19.99 for them, still a good deal but not as good.

The antenna is waterproof, but what about the connector? On the Symmetricon antenna that I have, the connection is made inside a tube, the top of which is sealed with a gasket. So unless you mount it upside down, water can't get in. As you say the listing isn't too good, but based on the picture that's there it looks like water could get into the connector.

I'd recommend any outdoor antenna connection be properly sealed in vulcanizing/Self-amalgamating tape.

Well crap, now the price of vulcanizing/Self-amalgamating tape will go up too....

LMAO. Yes, seems all it takes is to post a brand name on here and the eBay prices skyrocket.
Title: Re: Economical option for precision frequency reference?
Post by: Lightages on September 04, 2015, 03:22:16 am
I was just wondering, was the OP question actually answered? ;D

What is the best economical option for a precision frequency reference?
With my experience so far, the FE5680B seems to be it.

What is the easiest to use and have running and have accurate without worrying about being off because of age drift?
IMHO the bg7tbl GPSDO on ebay, any flavor, is the best bet.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 04, 2015, 04:02:52 am
I was just wondering, was the OP question actually answered? ;D

What is the best economical option for a precision frequency reference?
With my experience so far, the FE5680B seems to be it.

What is the easiest to use and have running and have accurate without worrying about being off because of age drift?
IMHO the bg7tbl GPSDO on ebay, any flavor, is the best bet.

I am the OP. I think the answer depends on what your specific needs are. They all stay accurate without drift - that's what the GPS is there for. Here is a breakdown of how I see it:

BG7TBL / 2014-12-09 -
  Pros: Smallest unit, good sensitivity on GPS receiver.
  Cons: Small frequency error. OCXO has a high failure rate in first 30 days. No management interface. Produced by someone who is semi-anonymous and not able or willing to answer questions about his product. No software to monitor. GPS chip is a UBlox non-timing chip, which has more jitter than their equivalent timing chips (like the one used in the Huawei).

Huawei/BG7TBL 2015-07-08 (Star4+ board)
  Pros: Excellent OCXO, Good management interface, excellent GPS sensitivity using UBlox timing application-specific GPS receiver module, coolest running unit. Simple mod to expose second 10M output (square wave)
  Cons: Requires minor change (solder two wires) to fix management interface mis-wiring from BG7TBL. Limited availability now it seems. No software to monitor.

"TRIMBLE"/BG7TBL 2015-07-17 -
  Pros: Good management interface.
  Cons: Insensitive GPS receiver. OCXO quality was on the low end (but still not bad). No software to monitor.

Lucent KS24361
  Pros: Great management interface compatible with Z38XX software. Ties with Huawei for quality of output.
  Cons: Big (two units, but can be hacked into one unit with a special cable and mod to expose the 10Mhz signal). Generates a ton of heat compared to all but the BG7TBL unit which is similarly hot. Poor sensitivity on GPS receiver. Crazy DB9 power connectors with funky latch. RS422 interface instead of RS232. 15 MHz primary output instead of 10. It has 10 MHz output, but it's reportedly relatively poor quality compared to the 15Mhz.

So personally, I prefer the Huawei/Star4+ board, with or without the BG7TBL strap-on hardware. My second choice would probably be the BG7TBL/2014-12-09 unit, because the frequency error isn't important to me, and it does make a nice compact unit and has good GPS sensitivity. My third choice would be the Lucent.

Title: Re: Economical option for precision frequency reference?
Post by: DimitriP on September 04, 2015, 04:30:29 am
For a box with no docs, no specs, no software and an abused looking OCXO to boot, no one should be paying more than $60-$70 for it.
But you know what they say ...opinions are like GPSDOs...everyone has one.....

 
Title: Re: Economical option for precision frequency reference?
Post by: EV on September 04, 2015, 01:17:50 pm
Huawei/BG7TBL 2015-07-08 (Star4+ board)
...
  Cons: Requires minor change (solder two wires) to fix management interface mis-wiring from BG7TBL. Limited availability now it seems. No software to monitor.

Can you give details or link for these changes?
Title: Re: Economical option for precision frequency reference?
Post by: carpelux on September 04, 2015, 05:18:17 pm
First: Hats of to your work motocoder (and all other that has given great information on all these devices).

I have followed the other thread about the BG7TBL but failed to really understand what modifications to do on the huawei flavor of the BG7TBL gpsdo to get communication with it. I failed to run ublox u-center, it kept resetting the satellites all the time and didn't show any fix, but I suppose that's because the computer only has read-only access to the receiver. Don't know if u-center will work after these modifications is done?
 
I received my sample of the BG7TBL 2015-07-08 from ebay a couple of days ago, and so far it seems to work very good. Haven't had that much time to evaluate it, but it got GPS lock within about 30 mins and has kept it that way. I have a Racal Dana 1998 (with option 04E) connected to it  and my visual checks shows it has been steady between 10.000000004 and 10.000000039 during the 5 days it has been running. I suppose it's really useless information, but I'm happy with both the gpsdo and the counter.

Anyway, more detailed information on the modifications would be very much appreciated.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 05, 2015, 06:46:40 am
For a box with no docs, no specs, no software and an abused looking OCXO to boot, no one should be paying more than $60-$70 for it.
But you know what they say ...opinions are like GPSDOs...everyone has one.....

What option out there is $60-$70?
Title: Re: Economical option for precision frequency reference?
Post by: Shock on September 05, 2015, 08:22:10 am
FYI the LUCENT/SYMMETRICOM Z3810AS, KS24361 has gone up to $200 now. 9 left.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 05, 2015, 05:11:13 pm
Huawei/BG7TBL 2015-07-08 (Star4+ board)
...
  Cons: Requires minor change (solder two wires) to fix management interface mis-wiring from BG7TBL. Limited availability now it seems. No software to monitor.

Can you give details or link for these changes?

Here are the details for the two simple mods that I have done to the Huawei.

The Huwai/"BG7TBL" 2015-07-08 is actually a Star4+ board from Oscilloquartz that BG7TBL has strapped onto a PCB of his design and jammed into an enclosure. The BG7TBL PCB is a nicely designed board that allows him to connect a variety of 3rd-party GPSDO and provide consistent front panel connections. He includes a MAX3232 chip in there so that internal TTL-level signals can be converted to RS-232 levels before connecting to the DB9, connection points for power, LEDs, and the BNC connectors.

In this post I will show you how to reconfigure the DB9 connector to connect to the actual RS232 management interface on the Star4+ board, as well as how to add a square wave output to the front panel. Since the actual GPSDO is a Star4+ board, the first thing I would recommend is to download the user manual for that which usagi links in this post:

https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg740339/#msg740339 (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg740339/#msg740339)

If you look near the bottom of this manual, you will see a diagram for a connector on the Star4+ board. THis is where we are going to be tapping into the various signals. Let's discuss the management interface first, as I think that's the mod most people will be interested in.

As the board comes from the eBay seller, the front panel DB9 is a "talk only" interface and is connected to an RS-232 level version of the Tx interface from the uBlox GPS chip. This will sort of let you run the uBlox u-center software. I say "sort of" because this software gets confused by the interface being effectively read-only, and it has some issues sometimes and much of the functionality doesn't work. However, it's enough to see the satellite strength and some basic stats. If having this sort of nice graphical interface is important to you, stop here, because you won't get that after the mod. If you proceed with this mod, you will (until some nicer software is available) just be able to use a serial terminal to connect to the board. However, you will have access to more information, including the state of the actual GPSDO, and the ability to set parameters such as the antenna delay. The board has a set of commands that are documented in the aforementioned manual; take a look at those to see what's possible.

On the Star4+ board is a Xilinx FPGA, which has inside it a soft-core processor. This processor is what actually implements the control logic of the GPSDO. It talks to the uBlox chip via a serial connection  on the uBlox, which is why BG7TBL was not able to route the uBlox Rx pin out to the DB9 connector. This soft-core processor has its own serial connection which we can talk to send commands and view status.

To proceed with the mod, remove the 4 screws from the front panel and slide out the board. The picture below shows a top-down view of the Star4+ board sitting on top of the BG7TBL adapter board. Note the black connector that the red arrow is pointing to. THis is where we are going to make our connections. Also note the arrow pointing to the uBlox chip. This is where the uBlox Tx connection is being made.
(https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=169636;image)

The next picture shows a detail view of the connector. The yellow wire is the connection to the management Tx pin, and the green wire is the connection to the management Rx pin. Solder some suitable wire there, and route these wires around to the bottom of the board. If you're interested in also adding the square wave output, you can also see the connection for that here.

(https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=169638;image)

Here is a close-up of the bottom side of the BG7TBL adapter board. Note the yellow and green wires, and the dangling red wire. The red wire is coming from the uBlox Tx pin, and used to connect to where the yellow wire connects now. These connections go through the MAX3232 chip, and then onto the front panel.

(https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=169640;image)

If you're also interested in adding a square wave output, this is what I did there. Remove the front panel, which is a simple matter of removing the nuts from the two BNC connectors and the one SMA connector. Drill a suitable size whole for your BNC. I purchased a BNC connector with a pre-attached pigtail off of eBay. It had an SMA connector on the other end, which I just snipped off. Re-attach the panel, add in your new BNC, and solder it to the location shown in the previous photo. There is a convenient spot to solder the ground/shield right there, so it's a very simple connection other than the fact that the connector pads are very small.

(https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=169642;image)

Now before you do this mod, you might want to have a look at the scope capture of the square wave output. It's not the nicest square wave in the world, and in particular note that the duty cycle is not remotely close to 50%. At some point I will probably come back and add a little daughterboard to convert the sine wave to a clean, 50% duty cycle square wave.

(https://www.eevblog.com/forum/testgear/economical-option-for-precision-frequency-reference/?action=dlattach;attach=169644;image)
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 06, 2015, 02:12:13 am
I was just wondering, was the OP question actually answered? ;D

What is the best economical option for a precision frequency reference?
With my experience so far, the FE5680B seems to be it.

What is the easiest to use and have running and have accurate without worrying about being off because of age drift?
IMHO the bg7tbl GPSDO on ebay, any flavor, is the best bet.

So far I've purchased a Nortel NTBW50AA for 80 USD shipped and a second Trimble unit which is a PCB with no case for 48 USD shipped. I also purchased cables to convert the various connectors on the two units to BNC for another 12 USD shipped. And lastly two Trimble GPS antennas which were 15.99 USD shipped each. I already had power supplies on hand. I have the Nortel unit fired up and running, the Trimble PCB has not yet arrived from china. The Nortel is a little large but is known to work extremely well, it has an even second output instead of 1 PPS but 1 PPS is on the board, a cut trace and jumper and you can have the 1 PPS if needed. In my case I really only care about the 10 MHz. The Nortel also has a DB9 factory installed and directly supports the Trimble diag software as well as Lady Heather. The other unit I will be receiving has a text based user interface, a DB9 just needs to be wired in. I will install it in a box when I receive it and after some aging time I plan to compare the two side by side. I already have both antennas installed on my tower outside with exact length runs of coax in to the shop.
I'd still like a rubidium based reference and when I can find one at a reasonable price I will pick it up. Clearly the rubidium is easier for most people to manage as it doesn't need an antenna however if you receive one off ebay you have no idea if it really is outputting 10 MHz or 1 PPS - they still technically need calibration. Also many of them are 10 to 20 years old. So as an only source I prefer a GPS based solution over rubidium. With a little effort and patience it should be no problem to purchase and setup a nice stable reference in your shop for under 100 USD. The Trimble based GPS units also seem to require less power then rubidium, my Nortel is 5 to 6 watts when warm.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 06, 2015, 04:09:06 am
I was just wondering, was the OP question actually answered? ;D

What is the best economical option for a precision frequency reference?
With my experience so far, the FE5680B seems to be it.

What is the easiest to use and have running and have accurate without worrying about being off because of age drift?
IMHO the bg7tbl GPSDO on ebay, any flavor, is the best bet.

So far I've purchased a Nortel NTBW50AA for 80 USD shipped and a second Trimble unit which is a PCB with no case for 48 USD shipped. I also purchased cables to convert the various connectors on the two units to BNC for another 12 USD shipped. And lastly two Trimble GPS antennas which were 15.99 USD shipped each. I already had power supplies on hand. I have the Nortel unit fired up and running, the Trimble PCB has not yet arrived from china. The Nortel is a little large but is known to work extremely well, it has an even second output instead of 1 PPS but 1 PPS is on the board, a cut trace and jumper and you can have the 1 PPS if needed. In my case I really only care about the 10 MHz. The Nortel also has a DB9 factory installed and directly supports the Trimble diag software as well as Lady Heather. The other unit I will be receiving has a text based user interface, a DB9 just needs to be wired in. I will install it in a box when I receive it and after some aging time I plan to compare the two side by side. I already have both antennas installed on my tower outside with exact length runs of coax in to the shop.
I'd still like a rubidium based reference and when I can find one at a reasonable price I will pick it up. Clearly the rubidium is easier for most people to manage as it doesn't need an antenna however if you receive one off ebay you have no idea if it really is outputting 10 MHz or 1 PPS - they still technically need calibration. Also many of them are 10 to 20 years old. So as an only source I prefer a GPS based solution over rubidium. With a little effort and patience it should be no problem to purchase and setup a nice stable reference in your shop for under 100 USD. The Trimble based GPS units also seem to require less power then rubidium, my Nortel is 5 to 6 watts when warm.

Nortel NTBW50AA goes on eBay, with antenna but not power supply, for exactly the same price as the options I listed above: $159. I do see a few standalone units for $80 in the sold items search, but they are not generally available at that price and that price does not include the nice antenna that the $159 package does.

So I don't think you're comparing apples to apples here. Let's say  you didn't have power supply on hand, but that one could be had for $15. So after looking and waiting on eBay for some time, you finally snag a deal on the $80 Nortel unit. Then you buy an antenna for $16, and the BNC converter for $6. Your at $115. Ok, you saved $54 with some smart shopping and by being willing to wait to find the right deal. Good on you. However, you also got an 8 channel GPS receiver with relatively poor GPS sensitivity. ALso, have you actually verified the Nortel unit supports the software you mention? A brief scan of the time-nuts mailing list shows a few posts saying there is some model of that (it's actually listed as "Symmetricon Nortel NTBW50AA" that does not.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 06, 2015, 04:24:41 am
I have Lady Heather connected to my Nortel unit as I type this. Started the program and it connected. To build a system for under 100 USD it would take time I do admit. I was more referring to the 48 dollar unit I picked up off ebay. The price has since gone up but they seem to go up/down quite often. They have been as low as 40 USD shipped. The cheaper one also has a newer 12 channel receiver based on posts over on time-nuts, hopefully it arrives soon.

I selected a price of 100.00 USD as to me that seemed to meet the "economical" request. Considering the price of quality test equipment maybe anything under $100 should be considered cheap.

btw, my Nortel/Trimble unit does not mention Symmetricon anywhere on it and is the version with a single PCB.

Maybe we could come up with a list of known working options that includes pictures for people so they can try to acquire the exact same hardware if they really want to get something going as cheap as possible instead of buying one of the ready to go solutions. I am buying various pieces myself as I find it more fun, others may just want to get something that plugs in and runs when it arrives.
Title: Re: Economical option for precision frequency reference?
Post by: EV on September 06, 2015, 05:47:19 am
Here are the details for the two simple mods that I have done to the Huawei.
...
...

Thanks motocoder!
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 06, 2015, 06:46:14 am
I have Lady Heather connected to my Nortel unit as I type this. Started the program and it connected. To build a system for under 100 USD it would take time I do admit. I was more referring to the 48 dollar unit I picked up off ebay. The price has since gone up but they seem to go up/down quite often. They have been as low as 40 USD shipped. The cheaper one also has a newer 12 channel receiver based on posts over on time-nuts, hopefully it arrives soon.

I selected a price of 100.00 USD as to me that seemed to meet the "economical" request. Considering the price of quality test equipment maybe anything under $100 should be considered cheap.

btw, my Nortel/Trimble unit does not mention Symmetricon anywhere on it and is the version with a single PCB.

Maybe we could come up with a list of known working options that includes pictures for people so they can try to acquire the exact same hardware if they really want to get something going as cheap as possible instead of buying one of the ready to go solutions. I am buying various pieces myself as I find it more fun, others may just want to get something that plugs in and runs when it arrives.

I'll be interested to see what the Trimble is when you get it. I suspects it's teh surplus board that is in the "Trimble" BG7TBL unit I tested. Hopefully not, because that one was at the bottom of my list in terms of features and bang for the buck.

I agree it's fun to assemble stuff. I had a lot of fun playing around with the Lucent unit, but now I really just want the space back on my bench.
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 06, 2015, 06:51:48 am
Here are the details for the two simple mods that I have done to the Huawei.
...
...

Thanks motocoder!

You're very welcome. We should both thank usagi for getting the Star4+ manual from OscilloQuartz, and edpalmer42 for numerous helpful posts on this topic.

BTW - you may want to refresh my post; I forgot to embed the picture of the bottom of the board.
Title: Re: Economical option for precision frequency reference?
Post by: voltsandjolts on September 13, 2015, 08:04:18 pm

I'd just like to point out a very cheap and stable reference for anyone like me who has fairly basic accuracy requirements. I only need an accurate reference intermittantly to calibrate my old but reliable OCXO based frequency counter. As has been discussed in this thread, the UBLOX LEA-6T has improved timing specs over some other UBLOX modules, can output a MHz signal locked to GPS atomic clocks and is available $30 on ebay complete with antenna.

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=lea-6t&_sop=15 (http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=lea-6t&_sop=15)

Unfortunately, neither of the timepulse outputs are wired outside the unit - so need to add some RG178 and BNC ($3)

OK, this unit has some nasty jitter but is it good enough to calibrate my frequency counter using a 10 second gatetime? I tested it against a (borrowed) Agilent 53230A with UOCXO option (nice!). I set the UBLOX output to 8MHz as recommened in datasheet for minimum jitter.

Answer: Over one hour the frequency spread was mostly within 4ppb and showed the Agilent to be 8ppb off frequency (well, that would need verified I guess).

So, I think LEA-6T is good enough for me.


Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 14, 2015, 03:26:59 am
Messed around with my Trimble/Nortel NTBW50AA for a bit today. I converted the Chip Clock/8X output from 9.8304 MHz to 19.6608 MHz and the even second PP2S output to a more normal 1 PPS output that has a positive going pulse.

The 19.6608 MHz clock is useful to me as it is one of the standard reference in options on my Agilent N1996A spectrum analyzer.

The 9.8304 MHz to 19.6608 MHz mod is very simple. The 19.6608 MHz signal is normally divided by two by U18 (74HC74). The divide is bypassed by lifting U18 pin 6 and running a jumper(white wire) from TP30 to TP33.

The PP2S signal is supplied to R82 by an output from the Xilinx chip, it has an input(from the Trimble chip) which is fed a more useful 1 PPS (TP13). I ran a jumper (yellow wire) from the 1 PPS signal going into the Xilinx chip to R82 which was rotated 90 degrees to allow connection to the jumper and disconnect the PP2S input.
The last mod was to lift pin 9 of U18 and run a jumper (blue wire) from pin 8 of U18 to TP29. This inverts the signal so that the 1 PPS signal pulse on the output is positive going.

All of the signals are phase locked to each other and that should be preserved just fine with this mod. The actual delay of the PPS signal would need to be measured but should be a consistent fixed value as I have read the PPS signal going into the Xilinx(from the Trimble chip) is fully corrected.

Hopefully someone else may find this mod useful and sorry for the crap quality pic, no daylight here right now to get a really nice shot.

edit - there seems to be more then version of this GPSTM around, my board is marked as a "NTBW50AA 10" on the front, on the back it says it is PN 45321-00. It is a single board design that I believe came from a Sprint site. It talks to Lady Heather etc with no problems.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on September 14, 2015, 05:27:11 am
What is the ocxo on your board?
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on September 14, 2015, 05:28:15 am
What is the ocxo on your board?

34310-T
Title: Re: Economical option for precision frequency reference?
Post by: evb149 on September 14, 2015, 07:19:57 am
FWIW in case others are interested in my initial experiences so far setting up the KS-24361 LUCENT RFTG-u units, after trying three other locations in the room (that didn't initially work), I was able to get the lucent units to work indoors on the top floor of a two story house using a 28dB gain mag-mount active patch antenna and I was seeing C/N ratios of 31, 31, 35, and 39 for the four satellites being tracked when last I checked.  Another +10 to +20 dB C/N would be nice to attain eventually but for the moment this is minimally adequate.
A location nearer the middle of the room worked better than near the window / corner / outside wall for me.  The initial antenna I have used is this one:
http://www.amazon.com/Waterproof-Active-Antenna-28dB-Gain/dp/B00LXRQY9A (http://www.amazon.com/Waterproof-Active-Antenna-28dB-Gain/dp/B00LXRQY9A)

I read: TFOM=3, FFOM=0 with a predicted 7.4us/initial 24 hrs holdover uncertainty was my recent reading after letting the units run for a few days with the poor antenna placement / type and not particuarly good signal quality.
I'll put up a proper timing type of outside antenna at some point to improve the reception.

The RS-422 outputs run between about +0.9V and +4V relative to GND with a 2.4 median level, so I was able to use a 5VDC VDD level MCU / USB-to-UART interface to connect the RS-422 UART / PPS signals to the PC or MCU for a quick test.

The 10VTP appears to be +17dBm relative to 50 ohms so 8.4Vp-p with a distorted sinusoidal waveform, I don't know if it is tracking the "17 vs 23" dBm level switches that affect the 15MHz outputs, I didn't check yet, but my switches are set to "17".

Thanks to all who have recommended these units and who have shared so much good information about them!


Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on September 23, 2015, 03:48:07 pm
Got what I think was a very ECONOMICAL Spectracom SecureSync on the bay. Can't wait to set it up...

Anyone have experience with these???

https://www.youtube.com/watch?v=VRM4EIeZykQ (https://www.youtube.com/watch?v=VRM4EIeZykQ)

http://spectracom.com/Desktopmodules/Bring2Mind/DMX/Download.aspx?EntryId=419&PortalId=0 (http://spectracom.com/Desktopmodules/Bring2Mind/DMX/Download.aspx?EntryId=419&PortalId=0)


Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on September 24, 2015, 01:38:28 pm
New Lucent KS-24361 RFTG-u info...

https://www.mail-archive.com/time-nuts@febo.com/msg74968.html (https://www.mail-archive.com/time-nuts@febo.com/msg74968.html)

Title: Re: Economical option for precision frequency reference?
Post by: motocoder on September 24, 2015, 02:16:51 pm
New Lucent KS-24361 RFTG-u info...

https://www.mail-archive.com/time-nuts@febo.com/msg74968.html (https://www.mail-archive.com/time-nuts@febo.com/msg74968.html)

So to summarize this for people that don't want to wade through the whole document. Someone has figured out how to modify the KS-24361 REF 0 unit to make it functionally equivalent to a REF 1 unit. You just need to come up with a surplus Motorola OnCore GPS unit from somewhere, and do a little SMD rework, and now you have the equivalent of a standalone REF-1 unit with the 10 MHz test-point output
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on September 24, 2015, 03:01:28 pm
Got what I think was a very ECONOMICAL Spectracom SecureSync on the bay. Can't wait to set it up...
very cool, expecting a teardown. Do you know what options it has?
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on September 24, 2015, 07:11:15 pm
yes... cool, probably not worthy of such a fine instrument, but I'll be trying my best... :-+

No option cards installed, and it has the standard OCXO, so nothing extremely exciting, but at least it doesn't have the downgrade TCXO  :phew:. I was thinking of doing a teardown with photos, or video. Spectracom claims it is impossible to upgrade the reference oscillator after manufacturing, but maybe they are not counting on an EEVblogger investigating that possibility. I noticed the unit weight increases by roughly a half pound with the high stability Rb Osc. installed. That does not sound like a surface mount device! Should be in my hands early next week some time.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on September 24, 2015, 07:30:47 pm
When i first was getting into this...
I saw a spectracom 9183(i think right model) gps freq std. Reading the manual i determined to have the rb option. I bid,  put a max bid of 205. And lost. Another one appeared bid first, max bid of 343... lost again. The only person bidding against me was the same person. I was upset.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on October 10, 2015, 11:34:06 pm
Finally received my Trimble unit a few days ago. It is the same or a very similar unit used in the BG7TBL trimble units. I have it mounted in a box and it has been running for a few days now. So far I have no complaints. While I have no primary source to compare it to the jitter between it and my Nortel has been under 30ns over a 24 hour period. My unit has the 63090 OCXO in it. The part # on the board itself is 57964-15. The board appears to use an Xemics 3330R GPS RF front end IC which feeds I/Q outputs to the processor for decoding.

The output from the command "*IDN?" is:

TRIMBLE,57964-15,86972377,V3.0.0.11-01

If you have one of these units or the equivalent BG7TBL unit you can force a site survey with the command "SYSTem:PRESet"
The board stores the last survey location and maintains it without power. However as motocoder mentioned earlier in this thread it does not store the elevation mask setting. At power on it always defaults to 5 degrees. If you're performing a site survey I'd set it to 10 to 20 degrees.
The default serial comm is 57600,8,N,1

You can enable once per second time packets to be output via the serial port if needed. It has two dual color LEDs on the bottom of the board that I moved to the front of my enclosure. I didn't want to install 4 LEDs and didn't have any dual color common anode LEDs so I cheated and cut the tips off some 5 MM opaque LEDs and then used CA(glue) to attach the original SMD LEDs to the tips of the 5MM LEDs - it is working great and they look like regular 5MM dual color LEDs in use.

The board requires 6 volts @ 1.8 amps during warmup and 0.85 amps after it is warm. It is a possible cheap option for people if they already have an antenna/power/box etc and like building stuff. I got mine for 48 USD shipped off ebay but the price has since gone up quite a bit. I do see there is a Symmetricom version of the same board for for 48 USD shipped though which is likely a potential good option.
If you want a complete solution it would be tough to beat the regular BG7TBL packages offered on ebay.

I also came across a working Cesium reference for 1K today - sadly it is out of my budget for a fun toy.

Attached a few pics of the unit. I've since ordered a black enclosure so I may swap the top and bottom halves so its totally black when it comes in next week.
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 11, 2015, 08:13:49 am
I do see there is a Symmetricom version of the same board for for 48 USD shipped though which is likely a potential good option.
If you want a complete solution it would be tough to beat the regular BG7TBL packages offered on ebay.

I believe this (http://www.ebay.com/itm/121761130751) is what you refer to? I've just bought one anyway. Time to dip my toe in the time-nuts water. Perhaps I should buy some RF connectors while I wait for it to arrive. What are they? SMA?
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on October 11, 2015, 08:20:10 am
I do see there is a Symmetricom version of the same board for for 48 USD shipped though which is likely a potential good option.
If you want a complete solution it would be tough to beat the regular BG7TBL packages offered on ebay.

I believe this (http://www.ebay.com/itm/121761130751) is what you refer to? I've just bought one anyway. Time to dip my toe in the time-nuts water. Perhaps I should buy some RF connectors while I wait for it to arrive. What are they? SMA?

Yep, that is the one. The mating connectors for the jacks on the board are MCX - this is the cable I used with the BNC connectors - http://www.ebay.com/itm/281313869844 (http://www.ebay.com/itm/281313869844)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on October 11, 2015, 08:03:56 pm
I have decided to sell the Lucent, BG7TBL Trimble, and BG7TBL units that I bought to do the test/evaluation.

 The two BG7TBL units come with the antenna and power supply that the eBay seller ships with them.

The Trimble unit has some ventilation holes in the case. I added these because its oven runs quite hot, and I was concerned about longevity of the other components in the case.

The Lucent comes with a high quality medical grade power supply to which I have afixed the DB9 power connectors with the appropriate latches. It also comes with a high quality, FTDI-based RS-422 to USB adapter and a DB9 adapter cable. I'll throw in a TNC to N patch cable as well.

PM me if intetested.
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 12:58:10 am
I know there are curious types around here, so I wanted to do this minor tear-down, actually, more a description of the interior of the Spectracom SecureSync unit. There is not really much to disassemble.

 I also wanted to test it right away for 100% functionality, and no error conditions. So it has been powered on for a little more than a week now,
 and has begun to settle down a bit. It does seem quite sensitive to room temperature change. I live in a canyon, so reception is poor here.
 Removing no less than 20 screws just to pop the cover while powered up to try to prevent any fluctuations in performance,
 but taking the cover off lowered the temperature severely. I started wondering about the thermal environment it had been designed for.
I think in a very warm rack space. The unit has 6 option slots on the rear panel, but each are perforated with plenty of holes.
So if all 6 option slots are filled with modules, the holes go away, and now added heat from the modules, all keeping it quite toasty inside.
 It does have a fan, but according to the instructions you may never hear it cycle on, except briefly at power on. I decided covering the option
 blanks with tape to isolate it from the outside air was a good idea. Fan still does not cycle on. Temp slightly higher now, and less fluctuation.

The GPS radio is a Trimble resolution T. The standard 10 mHz OCXO is a Russian made Morion MV-197. It has a Western Digital SSD of 1 GB.
 A small computer on board, an SOM-4455 by Advantek, featuring an AMD Geode LX 800 CPU, AMD CS5536 chipset, and 1GB of DDR-400 RAM.
The backup battery is a huge coin cell BR3032.  You can see the area of the board for the optional DC power, no fuse installed, and J33 not connected,
2 rather large inductors sitting there as well.

The Rubidium option jacks are there, no info about what that is. Even if you could ID it, Firmware for it would need to be installed.
According to Spectracom there are no upgrades after production. It appears to be a late 2012 production unit. The SSD is dated 9/5/12,
 the Morion MV-197 dated 12/28, which is the 28th week of 2012. All in all a pretty interesting, and quite sophisticated unit.

Here's a few photos of the interior, front, and rear. and some screen shots of interest.
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 12:59:36 am
more photos
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 01:01:01 am
more...
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 01:02:02 am
more
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 01:03:09 am
more
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 01:03:41 am
a few more
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 01:06:49 am
done
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on October 12, 2015, 01:28:40 am
Thanks for the teardown, I was wondering when you would post more pics...
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on October 12, 2015, 02:45:37 am
Hi,

Yes, testing came first.

 It appears possible to upgrade to the Morion Ultra LN OCXO double oven MV-209. Same footprint, just a tad taller.I doubt it would require a FW change.  I have to check the PS voltage, and whether Sine or CMOS output.

http://www.morion.com.ru/catalog_pdf/26_MV209.pdf (http://www.morion.com.ru/catalog_pdf/26_MV209.pdf)

Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on October 20, 2015, 05:54:49 am
I have been touring ebay for a distribution amplifier after reading that several people have used video amplifiers for the job. Decided on a Link Electronics video distribution amplifier that was 19.95 plus shipping. Opened it up, removed the eight 75 ohm output resistors and installed eight 49.9 ohm resistors. Set it to single ended mode, added an output terminator and then set the output level to 0 dBm into 50 ohms. The output looks good on my scope and spectrum analyzer. It will now be feeding 10 MHz to all of my devices. I liked this model because it had 8 outputs which should take me a long time to use and it uses less then 4 watts of power. Combined with the Trimble GPSDO the pair use under 10 watts which I think is fine to leave running 24/7 in the lab.

So anyone looking to run 10 MHz to a bunch of devices, check out the video amps on ebay.

EDIT:

After playing with this amp for a while I noticed I was able to see spurs above and below 10 MHz when using a very narrow RBW on my spectrum analyzer. Turns out they were 120 Hz above and below 10 MHz. A quick look at the amp explains while - it uses a full wave bridge rectifier, filter caps and no regulators. Internally it runs at plus and minus 10 volts. I cut some traces and wired in a 7805 and a 7905 with some caps. Before I did that I verified with an external supply that it seemed to run just fine at plus and minus 5 volts. The spurs are now gone and the output is cleaner. I may still get a 7808 and a 7908 next time I order from Digikey and wire them in to give a little more headroom. Turning the output all the way up though shows no clipping as it is. I believe the video input levels may be higher then the 1.5 vpp my GPSDO outputs.
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 24, 2015, 03:34:18 pm
Well, I got my Symmetricom module and some of those MCX-BNC leads :-+

Unfortunately the MCX socket for the GPS antenna appears to have been ripped from the board, and wasn't even to be found loose in the mail package. I will have to source one, but a bit of a PITA as it's a surface mount component. Also, there are two push buttons, MACT and RST. The MACT ones cap fell off and the spring contact vanished (if it was even there). Now those faults aren't so bad, but powering it up the DC/DC converter is ringing and no 5V, so no LED's or anything :(

I've powered up using the spare BT pin on the DBG connector using a 5V and everything kicks into life, but of course the oven isn't warming up :(

I've asked the seller for a return. He's initially responded with me finding the MCX connector locally and he will refund me that. Ok, but it was sold as used cosmetic wear and tear, fully functioning... If I didn't have a hot air station then I would be buggered.

So I'll carry on investigating this while I wait for his response and either return it for full refund or get a decent discount.

Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on October 24, 2015, 05:27:51 pm
Well that sucks. Even if you do get it working they should probably give you a full refund as its not quite a simple fix at this point. Would you be able to provide some pics of the board? The ones on ebay are pretty crappy.
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 26, 2015, 11:10:52 am
Well, one I took to send to the seller. Note the missing MCX and the dodgy looking MACT button. When I upturned the board the top fell off and the contact spring vanished  :rant:

(http://i.imgur.com/Eb1v00q.jpg)

The seller is telling me I could solder the socket with a normal iron "as its only 4 pins". I asked him how he would solder the 5th centre pin with an iron? hahaha. It's besides the point as it was advertised as working. Basically I've asked for a full refund or for him to send me a replacement. I've offered to return this at his cost of tracked delivery (£47), I somehow don't think he will want it back.

Nevertheless, I persisted with trying to get somewhere with it in the meantime. I found any voltage I applied to the 10A fuse (3.3V - 12V) would clamp my Rigol PSU at something around 3.3-4V. I had current limiting set to 2A but it would peak at about 1.6A. Ringing noise coming from the DC/DC converter and no indicator LEDs. The OCXO would get pretty toasty. There are various test points on board, 1.2V, 3.3V good, 5V was bad - less than 4V. A PWR test point going to the OCXO was around 8-9V even with only 5-6V supply. Another test point VREF is in the 4-5V range.

I found that not using the main power but the BT (battery?) connection on the 4 pin DBG (rx/tx) header with 5V flicked the board into life. Combining 2 supplies, 5V at BT and 6V for power in the ringing would stop when the OCXO got really hot and then would stop heating as the current dropped from 1.5A to 300mA or so. I can connect using serial OK and plenty of commands to play with. Looking at the diagnostic log this device was previously installed somewhere north of Tokyo back in 2014 ;)

When the DC/DC converter settled down I found I could remove the 5V BT supply and it would remain running. So I've been playing with the serial commands for now.
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 26, 2015, 12:17:29 pm
Some interesting serial logs:

Powered on and help command

Code: [Select]

Symmetricom Boot Code ver. 1.01.01


Press Enter to go to boot
Image1: [1.0.0.2] [454535 bytes] [valid checksum:0x20AFA24] [timestamp:3]
Image2: [1.0.0.1] [454535 bytes] [valid checksum:0x2142B89] [timestamp:2]

Loading Image1
UCCM-P > ?
*IDN?
ALARm:HARDware?
ALARm:OPERation?
DIAGnostic:OUTPut ON|OFF
OUTPut:ACTive:ENABle
OUTPut:ACTive:DISable
OUTPut:ACTive:HOLDover:DURation:THReshold <seconds>
OUTPut:ACTive:HOLDover:DURation:THReshold?
OUTPut:INACTive
OUTPut:INACTive?
OUTPut:STATe?
SYNChronization:HOLDover:DURation:STATus:THReshold <seconds>
SYSTem:PRESet
SYNChronization:TFOMerit?
LED:GPSLock?
SYNChronization:FFOMerit?
GPS:POSition N or S,<deg>,<min>,<sec>,E or W,<deg>,<min>,<sec>,<height>
GPS:POSition?
GPS:POSition:HOLD:LAST?
GPS:REFerence:ADELay <numeric value>
GPS:REFerence:ADELay?
GPS:SATellite:TRACking:COUNt?
GPS:SATellite:TRACking?
DIAGnostic:ROSCillator:EFControl:RELative?
SYNChronization:TINTerval?
DIAGnostic:LOG:READ:ALL?
DIAGnostic:LOG:CLEar
SYSTem:PON
OUTPut:MODE?
SYSTem:STATus?
SYSTem:COMMunication:SERial1:BAUD 9600|19200|38400|57600
SYSTem:COMMunication:SERial1:BAUD?
SYSTem:COMMunication:SERial1:PRESet
SYSTem:COMMunication:SERial2:BAUD 9600|19200|38400|57600
SYSTem:COMMunication:SERial2:BAUD?
SYSTem:COMMunication:SERial2:PRESet
OUTPut:STANby:THReshold <seconds>
changeSN
SYNChronization:REFerence:ENABLE LINK|GPS
SYNChronization:REFerence:DISABLE LINK|GPS
SYNChronization:REFerence:ENABLE?
STATus
POSSTATus
TOD EN|DI
TIME:STRing?
REFerence:TYPE GPS|LINK
REFerence:TYPE?
PULLINRANGE 0|1|2|...|254|255
PULLINRNAGE?
DIAGnostic:LOOP?
DIAGnostic:ROSCillator:EFControl:DATA GPS|<value>
DIAGnostic:ROSCillator:EFControl:DATA?
OUTPut:TP:SELection PP1S|PP2S
OUTPut:TP:SELection?
GPSystem:SATellite:TRACking:EMANgle <degrees>
GPSystem:SATellite:TRACking:EMANgle?
DIAGnostic:TCODe:STATus:AMASk
DIAGnostic:TCODe:STATus:OMASk
DIAGnostic:TCODe:ERRor:AMASk
DIAGnostic:TCODe:ERRor:OMASk
DIAGnostic:HOLDover:DELay
DIAGnostic:HOLDover:DELay?
GPS:SATellite:TRACking:IGNore <PRN>, ...,<PRN>
GPS:SATellite:TRACking:IGNore?
GPS:SATellite:TRACking:INCLude <PRN>, ...,<PRN>
GPS:SATellite:TRACking:INCLude?
GPS:SATellite:TRACking:<select>:ALL
Command Complete
UCCM-P >

The STATUS command
Code: [Select]

UCCM-P > status

                 - UCCM Slot STATE -



1-1. #Now ACTIVE STATUS ---------------- [OCXO Warm]
1-2. #Before ACTIVE STATUS ------------- [OCXO Warmup]
2-1. #Reference Clock Operation -------- [Not Used]
2-2. #Current Reference Type ----------- [LINK]
2-3. #Current Select Reference --------- [LINK0]
2-4. #Current Reference Status --------- [NOT SELECTED]
     #GPS STATUS ----------------------- [Unavailable]
     #Priority Level ------------------- [LINK > GPS]
     #ALARM STATUS
     #H/W FAIL ---------- [ LINK ]
     #OPERATION ALARM --- [ Antenna ]
3-1. PLL STATUS ------------------------ [Enable]
3-2. Current: PLL MODE ----------------- [OFFSET OBSERVATION MODE]
Command Complete
UCCM-P >

POSSTATUS

Code: [Select]
UCCM-P > posstatus
-----------------------------------------------------------------------------
1/6/1980 00:07:58
-----------------------------------------------------------------------------
 Position : LAT(N 34:44:0.000) LON(E 135:21:0.000) H(0.00 m MSL)
-----------------------------------------------------------------------------
 Geometry : PDOP(0.0) HDOP(0.0) VDOP(0.0)
-----------------------------------------------------------------------------
 Channel Status
   num of visible sats > 0
   num of sats tracked > 0
   ------ Receiver Channel State ------
     CH 0 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 1 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 2 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 3 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 4 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 5 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 6 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 7 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 8 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 9 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 10 >  SateID(0) TrackMode(code search) SigValue(0)
     CH 11 >  SateID(0) TrackMode(code search) SigValue(0)
-----------------------------------------------------------------------------
  Rcvr Status(1) :
-----------------------------------------------------------------------------
  Antenna Voltage: 6255 mV,  Antenna Current: 0 mA
-----------------------------------------------------------------------------
Command Complete
UCCM-P >

I note the Antenna Voltage appears to track my supply voltage (6.5V in this case). This is a bit concerning as my GPS Antenna is only 3.3-5V. I have found powering the board up with less than 5.5 volts results in an error in the log regarding insufficient current for the OCXO. I have measured the reported voltage directly at the (stripped) antenna connection and it is correct.

Finally the SYST:STATUS? command

Code: [Select]

UCCM-P > syst:status?
-------------------------------------------------------------------------------
090-03861-03   serial number W5609120082   firmware ver 1.0.0.2-01     LINK mode
-------------------------------------------------------------------------------
Reference Status __________________________   Reference Outputs _______________
   Ref 8KHz 0: [LOS]
                                              TFOM     9             FFOM     3
                                              UCCM-P Status[OCXO WARM]

>> GPS: [no ref]
......................................................... [ GPS 1PPS Invalid ]
Tracking: 0 ____   Not Tracking: 0 ________   Time ____________________________
                                              GPS      00:20:17 [?] 06 JAN 1980
                                              GPS      Invalid: not tracking
                                              ANT DLY  +0.000E+00
                                              Position ________________________
                                              MODE     Survey:      0% complete
                                                       Suspended: track <4 sats
                                              INIT LAT N  34:44:00.000
                                              INIT LON E 135:21:00.000
                                              INIT HGT           +0.00 m  (MSL)




ELEV MASK  5 deg
-------------------------------------------------------------------------------

Command Complete
UCCM-P >

Now for the provenance of this thing. Obtained from Hong Kong, the system status INIT LAT and LON show somewhere between KOBE and OSAKA in Japan (https://www.google.co.uk/maps/place/34%C2%B044'00.0%22N+135%C2%B021'00.0%22E/@34.7325662,135.2103989,10.5z/data=!4m2!3m1!1s0x0:0x0?hl=en) while the data recorded in the diagnostic logs (now overwritten - 500 line limit) show 2 site surveys in 2013 and 2014 some place called KOSHIGAYA north of TOKYO (https://www.google.co.uk/maps/place/35%C2%B052'30.2%22N+139%C2%B047'21.6%22E/@35.8784379,139.6008564,10.75z/data=!4m2!3m1!1s0x0:0x0?hl=en)  ;)
Title: Re: Economical option for precision frequency reference?
Post by: f1rmb on October 31, 2015, 11:09:52 am
Hi,

Some interesting serial logs:

...

I'm pretty interested with this board. Did you made some progress ?
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 31, 2015, 11:37:42 am
Yes. I've asked the seller to send me a new one. He wanted me to send this one back, so I asked him to arrange his own courier or go through the cheapest tracked royal mail options available to be. Obviously he didn't want that. He eventually settled for sending me another one out. We will see.

While sorting that out I found an MCX socket on an old junk board and swapped it over using hot air so I finally got to see some satellites. I'm using one of those cheap 3.3-5V "GPS Mouse" antennas stuck to a drainpipe outside my window.

However, the DC/DC converter was still troublesome and now the board would power up with only one supply but the oven wouldn't heat up and I couldn't get my 10MHz output.

It turns out the OCXO runs at 12V generated from a single 5V supply by a TI boost converter module (which is now kaput). I removed the module and powered up from with 12V directly to the OCXO and 5V supply and now everything is working.

I was considering making a dual supply for it but I've found the exact drop in replacement boost converter on AliExpress for around £3  :-+ 
Title: Re: Economical option for precision frequency reference?
Post by: f1rmb on October 31, 2015, 11:42:13 am
Hi,

Yes. I've asked the seller to send me a new one. He wanted me to send this one back, so I asked him to arrange his own courier or go through the cheapest tracked royal mail options available to be. Obviously he didn't want that. He eventually settled for sending me another one out. We will see.

While sorting that out I found an MCX socket on an old junk board and swapped it over using hot air so I finally got to see some satellites.

However, the DC/DC converter was still troublesome and now the board would power up with only one supply but the oven wouldn't heat up and I couldn't get my 10MHz output.

It turns out the OCXO runs at 12V generated from a single 5V supply by a TI boost converter module (which is now kaput). I removed the module and powered up from with 12V directly to the OCXO and 5V supply and now everything is working.

I was considering making a dual supply for it but I've found the exact drop in replacement boost converter on AliExpress for around £3  :-+

Great to read that. I guess I'll click the button ;-)

Did you connect the power supply (on the first step, before DC/DC troubles) like on the Trimble:
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)

Also, do you have some documentation for this board (tried a quick google search without real success until now).

Cheers.
---
Daniel
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on October 31, 2015, 12:13:43 pm
Great to read that. I guess I'll click the button ;-)
Oh yes, hopefully you won't have any trouble. They are sold as working after all. But it's well worth it even if you have the hassle I had.
Quote
Did you connect the power supply (on the first step, before DC/DC troubles) like on the Trimble:
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)
Yes. I started at 5V at the fuse and current limiting going up in steps to 12V, also down to 3.3V. I just had bad switching noise and the input circuit clamping my PSU voltage really low. Even with 12V it never got above 4V at the fuse. Boost converter eventually totally failed. (Not at 12V I might add - I had it running at 5.5-6V all this time to supply enough current to prevent reported OCXO failure, but it should really run at 5V alone)

Quote
Also, do you have some documentation for this board (tried a quick google search without real success until now).

Cheers.
---
Daniel
I'm looking but can't find anything specific. It does appear this board is a direct replacement for the Trimble though.
Title: Re: Economical option for precision frequency reference?
Post by: f1rmb on October 31, 2015, 12:18:14 pm
Great to read that. I guess I'll click the button ;-)
Oh yes, hopefully you won't have any trouble. They are sold as working after all. But it's well worth it even if you have the hassle I had.
Quote
Did you connect the power supply (on the first step, before DC/DC troubles) like on the Trimble:
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)
Yes. I started at 5V at the fuse and current limiting going up in steps to 12V, also down to 3.3V. I just had bad switching noise and the input circuit clamping my PSU voltage really low. Even with 12V it never got above 4V at the fuse. Boost converter eventually totally failed. (Not at 12V I might add - I had it running at 5.5-6V all this time to supply enough current to prevent reported OCXO failure, but it should really run at 5V alone)

Quote
Also, do you have some documentation for this board (tried a quick google search without real success until now).

Cheers.
---
Daniel
I'm looking but can't find anything specific. It does appear this board is a direct replacement for the Trimble though.

Okay, many thanks for all these informations, I guess I'll order one board later today ;-)

EDIT: Ordered :-)

Cheers.
---
Daniel
Title: Re: Economical option for precision frequency reference?
Post by: f1rmb on November 01, 2015, 05:06:20 pm
Hi,

Great to read that. I guess I'll click the button ;-)
Oh yes, hopefully you won't have any trouble. They are sold as working after all. But it's well worth it even if you have the hassle I had.
Quote
Did you connect the power supply (on the first step, before DC/DC troubles) like on the Trimble:
http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438 (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438)
Yes. I started at 5V at the fuse and current limiting going up in steps to 12V, also down to 3.3V. I just had bad switching noise and the input circuit clamping my PSU voltage really low. Even with 12V it never got above 4V at the fuse. Boost converter eventually totally failed. (Not at 12V I might add - I had it running at 5.5-6V all this time to supply enough current to prevent reported OCXO failure, but it should really run at 5V alone)

Quote
Also, do you have some documentation for this board (tried a quick google search without real success until now).

Cheers.
---
Daniel
I'm looking but can't find anything specific. It does appear this board is a direct replacement for the Trimble though.

   Did you measured the output signal level ? I'm looking to add an output buffer.

Cheers.
---
Daniel
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on November 01, 2015, 11:55:37 pm
~1.5V p-p, 50 ohms IIRC when I had 12V going to it. I have it put aside for now waiting for the replacement.
Title: Re: Economical option for precision frequency reference?
Post by: f1rmb on November 01, 2015, 11:57:24 pm
Hi,

~1.5V p-p, 50 ohms IIRC when I had 12V going to it. I have it put aside for now waiting for the replacement.

Excellent. Thanks again for everything. Can't wait to receive mine and start playing with.

Cheers.
---
Daniel
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 14, 2015, 07:31:14 pm
OK, I'm looking to jump in on this bandwagon.  So here what I think my options are..

1. If I buy  this Trimble system (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438) for $119, I just need a box and GPS antenna or
2. If I buy this Symmetricon unit (http://www.ebay.com/itm/121761130751) for $49, I'll also need a PSU and the pigtails.

Is the Trimble the better buy? Or has someone got a better suggestion?

Thanks
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 14, 2015, 08:47:09 pm
OK, I'm looking to jump in on this bandwagon.  So here what I think my options are..

1. If I buy  this Trimble system (http://www.ebay.com/itm/Trimble-GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-/181777773438) for $119, I just need a box and GPS antenna or
2. If I buy this Symmetricon unit (http://www.ebay.com/itm/121761130751) for $49, I'll also need a PSU and the pigtails.

Is the Trimble the better buy? Or has someone got a better suggestion?

Thanks

What will be your ultimate use for the device? If you are only interested in 10 MHz I'd recommend looking for a Nortel NTBW50AA - it has a cleaner 10 MHz with less phase noise and works with Lady Heather. It is much bigger though.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 15, 2015, 02:02:33 pm
FYI the LUCENT/SYMMETRICOM Z3810AS, KS24361 has gone up to $200 now. 9 left.

Last one is up for sale.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 15, 2015, 02:12:20 pm
I have been touring ebay for a distribution amplifier after reading that several people have used video amplifiers for the job. Decided on a Link Electronics video distribution amplifier .

This is what mine looks like, Extron ADA 6 300 MX HV, bit excessive but hey. I was originally going to get it for a Frequency Electronics Inc FE-5680A Rubidium standard, happy with my LUCENT/SYMMETRICOM Z3810AS, KS24361 RFTG/GPSDO instead.

(http://www.gearsourcecdn.com/gearsource/v5/catalog/listing/normal/f4143419-38cd-46d7-bfc8-41b79ba64365.jpg)
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 16, 2015, 06:57:06 am
I have been touring ebay for a distribution amplifier after reading that several people have used video amplifiers for the job. Decided on a Link Electronics video distribution amplifier .

This is what mine looks like, Extron ADA 6 300 MX HV, bit excessive but hey. I was originally going to get it for a Frequency Electronics Inc FE-5680A Rubidium standard, happy with my LUCENT/SYMMETRICOM Z3810AS, KS24361 RFTG/GPSDO instead.

Very nice - you're going to need a lot of equipment to connect to all those ports.

btw, have you checked to see how clean the signal coming out is versus what is going in? With mine I can't see too much on my spectrum analyzer however when I feed the 10 MHz into some devices I can see that the output isn't as clean(but its always bang on frequency!). I can generally see a small difference with and without the amplifier. The devices I have experimented with are an HP8714C network analyzer and an HP 8921A service monitor.
I can also see small differences between my cheapie Trimble GPSDO and the Nortel unit - the Nortel is cleaner.

The one device I need to keep experimenting with is my N1996A spectrum analyzer. The noise floor specs are only specified for its internal oscillator and are generally not as good with an external reference(it claims anyway). However instead of using 10 MHz in it will also accept 1 PPS. I can't help but wonder if possibly 1 PPS might end up cleaner.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 16, 2015, 11:58:26 am
This is what mine looks like, Extron ADA 6 300 MX HV, bit excessive but hey. I was originally going to get it for a Frequency Electronics Inc FE-5680A Rubidium standard, happy with my LUCENT/SYMMETRICOM Z3810AS, KS24361 RFTG/GPSDO instead.

Very nice - you're going to need a lot of equipment to connect to all those ports. btw, have you checked to see how clean the signal coming out is versus what is going in?

I have 5/10/15Mhz references and about half a dozen devices with 10Mhz external reference inputs, haven't done anything yet with it, but I believe the op amps are fairly high bandwidth and should give good results. This model is the more expensive version, though I only paid about $10 for the unit.

Here is a great video by Gerry Sweeney showing the unit. My source signals are very clean, incomparable to what he is using, also I don't have to gut the power supply in my situation. I was thinking of other ideas like on some of the outputs increasing the gain or making some attenuated.

I don't have a SA suitable just FFT on the 100MHz oscilloscope and a low frequency SA. I can't seeing it being too much of a problem though but I'll guess I will find out eventually.

https://www.youtube.com/watch?v=chrzrod3tQY (https://www.youtube.com/watch?v=chrzrod3tQY)
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on November 16, 2015, 02:17:30 pm
I have been touring ebay for a distribution amplifier after reading that several people have used video amplifiers for the job. Decided on a Link Electronics video distribution amplifier .

This is what mine looks like, Extron ADA 6 300 MX HV, bit excessive but hey. I was originally going to get it for a Frequency Electronics Inc FE-5680A Rubidium standard, happy with my LUCENT/SYMMETRICOM Z3810AS, KS24361 RFTG/GPSDO instead.

(http://www.gearsourcecdn.com/gearsource/v5/catalog/listing/normal/f4143419-38cd-46d7-bfc8-41b79ba64365.jpg)

Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 17, 2015, 08:43:14 am
Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec (http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec)
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 17, 2015, 12:44:58 pm
What will be your ultimate use for the device? If you are only interested in 10 MHz I'd recommend looking for a Nortel NTBW50AA - it has a cleaner 10 MHz with less phase noise and works with Lady Heather. It is much bigger though.
Steve, I took your advice and ordered a Nortel NTBW50AA from eBay, it needs a 24-48 volt power supply which gets up to 75 Watts when the heater is on full.  I found this power supply (http://www.allelectronics.com/make-a-store/item/ps-2432/24vdc-3.2a-switching-power-supply/1.html) but it would be running at 100% at 75 Watts which seems a bit tight, I'll keep looking but any suggestions are welcome.
Title: Re: Economical option for precision frequency reference?
Post by: carpelux on November 17, 2015, 01:30:25 pm
Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...
It isn't really that much work. I have one, and if I remember correctly it's replacement of only 15 resistors.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 17, 2015, 02:19:24 pm
Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...
It isn't really that much work. I have one, and if I remember correctly it's replacement of only 15 resistors.

Just saw w2aew did a distribution amp video yesterday some might find interesting.

https://www.youtube.com/watch?v=PjFr5YfxfLE (https://www.youtube.com/watch?v=PjFr5YfxfLE)
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 17, 2015, 04:52:43 pm
What will be your ultimate use for the device? If you are only interested in 10 MHz I'd recommend looking for a Nortel NTBW50AA - it has a cleaner 10 MHz with less phase noise and works with Lady Heather. It is much bigger though.
Steve, I took your advice and ordered a Nortel NTBW50AA from eBay, it needs a 24-48 volt power supply which gets up to 75 Watts when the heater is on full.  I found this power supply (http://www.allelectronics.com/make-a-store/item/ps-2432/24vdc-3.2a-switching-power-supply/1.html) but it would be running at 100% at 75 Watts which seems a bit tight, I'll keep looking but any suggestions are welcome.

When they wrote that spec they were talking about some worst case in rush current I am sure. When I tested mine it used 12 watts when warming up and about 9 watts after that. I use a good quality 24 vdc 0.5 amp wall adapter. That is what I had on hand but if buying new I would get one with a slightly higher current rating so it wasn't operating at 100% capacity when the OCXO is warming up. Absolutely no problems at all and it has been running for months and turned on/off many times. I also added a small rubber o-ring to one of the existing holes in the back of the unit and ran a power cord through it which leads to a 2.1mm connector. The wall adapter has the mating connector which keeps things nice and simple.
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on November 17, 2015, 07:20:18 pm
Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec (http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec)


I was aware, but still nice to see the 300, or 400mHz bandwidth. Getting the boards out/in seems to be most of the work for swapping out the terminating/source resistors.

Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on November 18, 2015, 12:07:57 am
Are you planning to mod that for 50 ohm in/out? Lots of work. I haven't used, or modded mine yet...

Yeah that is the plan to initially convert it to impedance match as shown in the video, I'll look at gain at the same time. I don't think there is too much work involved, it just depends how far I take it. Makes for a nice project box either way.

In case you weren't aware there is some specs on it here.
http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec (http://www.extron.com/product/product.aspx?id=ada6300mxhv#spec)


This might be a dumb question but why the high bandwidth ? Don't most instruments add low pass filtering on their "REF" inputs ?
I picked up an el cheapo chinese video distribution amp from fle-bay, ya it's 75 ohms but so far none of my HP gear seem to mind the slight impedance mismatch. 
Title: Re: Economical option for precision frequency reference?
Post by: bson on November 18, 2015, 07:03:24 am
Heads-up: there's a pile of 8 (7 now :)) Spectracom 8140 distribution amplifiers on eBay right now:
http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb (http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb)

One input, five outputs - four rear and one front.
Title: Re: Economical option for precision frequency reference?
Post by: Shock on November 18, 2015, 07:32:45 am
This might be a dumb question but why the high bandwidth ? Don't most instruments add low pass filtering on their "REF" inputs ? I picked up an el cheapo chinese video distribution amp from fle-bay, ya it's 75 ohms but so far none of my HP gear seem to mind the slight impedance mismatch.

You mean the bandwidth of the CLC409 op amp in the Extron in particular? Well I'm no expert but it's a good indicator that signal fidelity issues at 10MHz will be non existent, if compared to say an op amp which has a lower bandwidth than the input signal, gain will be affected and since it's operating outside it's parameters it's going to exceed it's noise specifications. I can't tell you if this would make it totally unusable plugged into a reference input (as they aren't that fussy on signals) but if you want to use your distribution amp for higher frequencies you're going to hit a wall sooner or later.

About the impedance, well RF commonly uses 50 Ohm cabling and termination so we are just matching that. Mismatched impedance is going to affect the gain and unterminated it can cause reflections/superstitions of the source signal. Will it matter for a 10MHz ref input? Well guess it depends how clean your source and how fussy your ref input is.
Title: Re: Economical option for precision frequency reference?
Post by: SoundTech-LG on November 20, 2015, 08:13:24 pm
Heads-up: there's a pile of 8 (7 now :)) Spectracom 8140 distribution amplifiers on eBay right now:
http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb (http://www.ebay.com/itm/Spectracom-8140-Frequency-Distribution-Amplifier-10Mhz-Input-Eight-Available-/221943556149?hash=item33acdde835:g:HRYAAOSwdvpWDWDb)

One input, five outputs - four rear and one front.

but, don't forget, you'll need the Spectracom Line Taps, and/or the Versa Taps to fully utilize the system. as intended...  you can also modify it to remove the +12 Volts DC riding on the rear panel outputs.
http://spectracom.com/documents/instruction-manual-model-8140/attachment (http://spectracom.com/documents/instruction-manual-model-8140/attachment)

Title: Re: Economical option for precision frequency reference?
Post by: bson on November 20, 2015, 10:53:20 pm
Good catch!  Wouldn't have noticed until I checked the output...  Bought a couple of taps to go with it.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 23, 2015, 06:17:13 pm
Got my NTBW50AA now and have ordered a PSU; thinking I'll copy the mods that Steve has done for 1 pps etc.  One question though, is the RS232 'real' RS232 (i.e. does it need + and - signals) or is it TTL?  It says it complies with the RS232-E standard but that seems to be something to do with rise times and noise.  I can already do TTL RS232 but I'll need to buy a cable to do 'real' RS232.
Title: Re: Economical option for precision frequency reference?
Post by: moya034 on November 23, 2015, 06:43:37 pm
If you want to put your frequency standard(s) and measurement ability to the test, the ARRL regularly sponsors a frequency measuring contest. http://www.arrl.org/frequency-measuring-test (http://www.arrl.org/frequency-measuring-test)
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 23, 2015, 07:06:59 pm
The Nortel unit is real, old school RS232 from the DB9 on the front.
Title: Re: Economical option for precision frequency reference?
Post by: bson on November 24, 2015, 04:30:28 am
Received the Spectracom 8140 and a couple of line taps, and it works perfectly.  My Thunderbolt outputs sinusoidal AC while the taps output sinusoidal DC.  The front BNC outputs a DC square wave that can be divided using the front buttons.  I'll be putting this to good use.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 27, 2015, 12:38:19 pm
I may get a chance to test out my NTBW50AA today.  I bought it with the (perhaps slightly naive) idea that I could use the 10 MHz output as an external clock input to stuff like my N1996A and E4433B to get super accuracy.  Some research has shown that, unless the signal from the NTBW50AA plus distribution amp is better (lower phase noise and less jitter) then this is not a good idea so, until I do more research on that topic, I will use the 10 MHz output to check the calibration of my gear.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 27, 2015, 05:00:24 pm
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 27, 2015, 07:25:12 pm
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on November 28, 2015, 06:30:12 pm
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
Well duh!  That worked!  Thanks Steve :D
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 28, 2015, 09:34:35 pm
Unless its actually in use you can do the easy solution and just change the usb serial port to com1 - then the default LH settings will work fine.
Well duh!  That worked!  Thanks Steve :D
I believe the issue with Windows 10 is that they've changed the way 'My Documents' works and have some weird protection for where programs are allowed to access files from.  Steve's suggestion allowed LH to just use the defaults.

Excellent - lady Heather is a rather old school program, I run it on an old netbook running XP.
Btw your N1996A claims it can use PP2S for an external reference but it actually works with PPS only.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on December 01, 2015, 12:19:08 am
Did a test run with the antenna outside on a pole on my lawn just to make sure it was all working - it was, I'll post a picture tomorrow.  Now to do the proper installation but I need to do the modifications that Steve suggested to get 1 PPS out of the front panel.
Title: Re: Economical option for precision frequency reference?
Post by: Lightages on December 01, 2015, 01:48:00 am
I have been running my BG7TBL / 2014-12-09 for quite a while now and it is working fine. I have been trying to get it working as a source for an NTP server using the instructions at: http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html (http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html)

I cannot get the receiver t change its settings to match the requirements to work at 4800 baud and use only $GPRMC sentences. I am using the u-center software but none of the settings I send take hold. With the default settings the NTP server software does not use the GPS as the clock.

Any suggestions?
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on December 01, 2015, 05:48:24 pm
OK, here's some pictures for y'all.  Does everything look OK from the data?

[Edit] OK, let me ask the question in a different way. Can anyone help me to interpret the data I'm seeing?  Given my interest in knowing that the Nortel box is giving me accurate timings, what do these indications tell me...

PPS^ -0.293456 ns
Osc^ 11.567843 ppt

Thanks in advance.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on December 07, 2015, 03:58:22 am
Did another small mod to my Nortel NTBW50AA that I've been meaning to do for a long time now. Instead of messing with the SMB connectors on the front I drilled a few holes on the back of the chassis and mounted BNC connectors for the GPS antenna in, 1 PPS and 10 MHz outputs. If you mount them on the back of the chassis you only need to drill through one layer of steel, use a step bit and the drilling is very easy. A few runs of coax cable run neatly under the PCB soldered to the SMB jacks or any other proper point on the PCB and you're done.
You can also see my power cable that runs through a rubber grommet installed in an existing chassis hole. The cable goes to a 2.1mm connector so I can use a 24 VDC wall adapter to power the unit.
Title: Re: Economical option for precision frequency reference?
Post by: Bryan on December 07, 2015, 11:49:52 am
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
Title: Re: Economical option for precision frequency reference?
Post by: Gandalf_Sr on December 28, 2015, 07:40:43 pm
Getting a bit frustrated, I'm trying to make Lady Heather talk to my NTBW50AA.  I bought a USB-RS232 cable and it installs on my Windows 10 system as COM4.  I'm pretty sure the cable connections are good but all that happens when I start LH is it says 'NO COM1 SERIAL PORT DATA SEEN' - I'm now trying Windows 8 compatibility mode and am running LH as Admin.

I added a heather.cfg file with nothing but '/4' in it but I still get the message about COM1 when LH starts up, I also tried typing in '/4' at the command interface.  I messed with various setting for the port - current settings are 9600, 8 bit, no parity, 1 stop bit

Any suggestions anyone?

[EDIT1] It seems it's a Lady Heather problem.  I have found the serial port setting and it's 19,200,7,Odd,1, and I think XOn/XOff, with these settings I can connect to Port 4 and then when I type '1' it responds with "E-113>

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
Bryan, thanks for the input.  I did get Lady Heather working on Windows 10, the issue is that the OS protects itself by not allowing unknown software to read from the actual location it's installed in so the instructions to place the Heather.cfg file in the same folder as the .exe file are wrong but, in fact, the '?' function tells you (all the way at the end), that the heather.cfg file needs to be in c:\user\<yourname>\OneDrive\Documents and when the file is placed there, it works. There are some issues if you try to change screen resolution but that's OK.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on December 28, 2015, 09:50:00 pm
I also had problems with Lady Heather. Tried different com port settings with her AND windblows 7. Ended up installing an old serial I/O board in one of the slots so that it would be com1.

 
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on December 31, 2015, 12:49:43 am
Due to a GPSDO sickness and too much time spent trolling ebay I bought another GPSDO. This is an HP 58540A - likely built to compete with the Trimble Thunderbolt.
It has an SCPI interface, it doesn't provide a ton of functions and is pretty basic overall. It uses a single 24 VDC supply and has a switching supply under the timing board which provides the needed voltages. I need to run it for a month or two before really seeing how it compares with my Trimble units.

Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on December 31, 2015, 12:55:24 am
I wonder what the trimpot does?
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on December 31, 2015, 01:05:45 am
I wonder what the trimpot does?
Probably something boring like setting the 10 MHz output level.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on December 31, 2015, 01:57:26 am
That makes sense, I believe that they do that in the lucent boxes.
Title: Re: Economical option for precision frequency reference?
Post by: N8AUM on December 31, 2015, 02:02:25 am
cool serial # the osc. !
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on December 31, 2015, 02:19:09 am
cool serial # the osc. !

Yeah, not sure how many of these they made. Google doesn't give too much info but the others I have seen use a different OCXO. The PCB layout fits several different OCXO models. It would be nice to upgrade it to something newer with lower phase noise but the odds of finding one that is drop in compatible with the hardware and firmware seems pretty slim.
Title: Re: Economical option for precision frequency reference?
Post by: dannyf on December 31, 2015, 03:10:40 pm
Quote
But what I'd really like is if someone can give me some practical suggestions on what is the most practical way to set up a good frequency reference - what is needed, and what's the best place to source one.

A few approaches, depending on what you want to do:

1) (VC)TCXO: usually good for 2.5ppm max - and typically < 0.5ppm at room temperature. Cheap and lots of frequency options;
2) GPS: slightly more expensive, but many are programmable so you can generate whatever frequencies you so desire.

I used a hybrid approach: I built a platform that adjusts a VCTCXO's output to a GPS. Once caliberated, that VCTCXO can operate without the GPS. Done on a PIC16F684 but should be easily adopted onto other platforms, as it is essentially a phase comparator.
Title: Re: Economical option for precision frequency reference?
Post by: Bryan on January 01, 2016, 09:40:53 pm

Have my Nortel working fine with LH on Windows 10 on Com 1. You may want to try a download of tboltmon.exe and try a hard or cold reset. I assume your ports in device manager are set properly. Mine are 9600,8,none,1. no flow control.
Bryan, thanks for the input.  I did get Lady Heather working on Windows 10, the issue is that the OS protects itself by not allowing unknown software to read from the actual location it's installed in so the instructions to place the Heather.cfg file in the same folder as the .exe file are wrong but, in fact, the '?' function tells you (all the way at the end), that the heather.cfg file needs to be in c:\user\<yourname>\OneDrive\Documents and when the file is placed there, it works. There are some issues if you try to change screen resolution but that's OK.

Yes, I noticed the same thing when trying to adjust the screen resolution , it will crash. Too bad it has not been updated since 2013, I think it is a great program. Would be great if it could be upgraded to incorporate some of the other GPSDO boxes out there. 

Another tip if I could share is to do a Autotune of the oscillator after it has been running for a number of months "&" then "A"
Title: Re: Economical option for precision frequency reference?
Post by: _Andrew_ on January 02, 2016, 03:25:37 am
Stumbled across these OCXO & GPS TCXO reference oscillators from Total Frequency Control

http://www.tfc.co.uk/products.php?CategoryID=3&gclid=CKmYp_-TisoCFRUTGwodmu4Bbw (http://www.tfc.co.uk/products.php?CategoryID=3&gclid=CKmYp_-TisoCFRUTGwodmu4Bbw)

http://www.tfc.co.uk/products.php?CategoryID=6&SubID=3 (http://www.tfc.co.uk/products.php?CategoryID=6&SubID=3)



 
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on January 04, 2016, 05:15:21 am
Thought I would compare the 1 PPS outputs from the three GPSDO's I have here.

The blue trace is the Nortel NTGS50AA which is the trigger channel
The yellow trace is the cheapie Trimble 57964-15 with 63090 OCXO
The purple trace is the HP 58540A

The scope has been running on infinite persistence for a few hours.
You can see the jitter on the HP is probably double what it is on either of the others(I have triggered on the Trimble with similar results).
I have changed the antenna delay to get them to be reasonably close on the scope so it is easier to see. By default the Nortel leads the Trimble by roughly 500ns which leads the HP by 100ns. So even with 3 GPSDO's I have no idea when the pulse really occurs :)
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on January 04, 2016, 06:54:33 am
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on January 04, 2016, 07:22:41 am
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed

The Rb's I have here don't have a 1 PPS output. I can watch the 10 MHz out but they will all wander a little as none are at exactly 10 MHz and it isn't possible to set them perfectly I don't think. The rate of wander is likely constant though which is what counts.
Title: Re: Economical option for precision frequency reference?
Post by: Bryan on January 04, 2016, 09:55:07 am
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed


Taking this into consideration what is the best way to "adjust" a RB to a GPSDO or is it really feasible to do so considering the GPSDO is better long term, but suffers from short term stability.
Title: Re: Economical option for precision frequency reference?
Post by: awallin on January 04, 2016, 01:24:34 pm
Taking this into consideration what is the best way to "adjust" a RB to a GPSDO or is it really feasible to do so considering the GPSDO is better long term, but suffers from short term stability.

PI-controller that looks at the difference between the GPSDO and Rb phase (either at 10MHz or 1PPS) and steers the Rb with a DAC. Time constant for a bad Rb-clock maybe hours, for a good one 1-2 days.
http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif (http://www.thinksrs.com/assets/instr/PRS10/PRS10diag2LG.gif)

The measurement of GPSDO vs Rb needs to be quite good. 9-digit/s frequency counter at least.
You'd want the GPSDO vs Rb measurement noise to reach an ADEV of 1e-12 (the limit for a typical Rb clock) a bit before the PI-loop time-constant, maybe at 1000s, so a 1PPS measurement good to 1ns that averages down as about 3e-9/tau should work.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on January 04, 2016, 04:56:49 pm
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed


Taking this into consideration what is the best way to "adjust" a RB to a GPSDO or is it really feasible to do so considering the GPSDO is better long term, but suffers from short term stability.

In the Temex LPFRS user manual it suggests using a GPSDO as a reference for an Agilent 53131A frequency counter. Being they have an analog voltage adjust this might be as stable as you can reasonably expect.
Title: Re: Economical option for precision frequency reference?
Post by: edpalmer42 on January 04, 2016, 10:04:56 pm
Now do the same test with 3 of your Rb oscillators.  You'll be shocked by the difference!  :o  Over a period of a few hours, the Rb oscillators are more stable than the GPSDOs.  It's only over longer time frames that the long-term frequency stability of the GPSDO starts to show its advantage over the Rb standard.

Of course, we have to remember that these GPSDOs are not optomized to give the lowest possible jitter.  You could make the time constants longer, but there are tradeoffs there too.  The same applies to the Rb units.  Low jitter just wasn't one of the design requirements.

Ed


Taking this into consideration what is the best way to "adjust" a RB to a GPSDO or is it really feasible to do so considering the GPSDO is better long term, but suffers from short term stability.

To do a one-time adjustment, the best way that I know is to use a time interval counter or DSO to measure the time from the rising edge of the GPSDO to the rising edge of the Rb.  It doesn't matter if it's 1 PPS or 10 MHz, but a square wave signal is best.  Note the time interval and then watch it over many minutes.  If the time interval increases, the Rb is falling behind the GPSDO, so increase its frequency a bit.  If the time interval decreases, the Rb is overtaking the GPSDO so slow it down.  If you log the time interval and the length of time between measurements, you can calculate the frequency difference.  The resolution of your measurement will be determined by the resolution of your time interval counter and the time between measurements.  A one nanosecond counter and measurements one hour apart gives you a resolution of < 3e-13.  The long interval between measurements helps average out the GPSDO's jitter.  This type of measurement can be made manually or you can collect the data electronically.

If you want to discipline the Rb to the GPS, that's a totally different situation.  I've never really understood the advantages to that (other than the technical challenge).  The only situation where I can see an advantage is if you have really poor GPS reception and you want your standard to maintain service through the outages.  Other than that, you can build an OCXO-equipped GPSDO that provides short-term performance that's limited only by the OCXO itself and long-term performance that's limited by GPS itself.  Both are better than the Rb's performance.

Ed
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on January 04, 2016, 10:23:27 pm
I did the quick tuning using my frequency counter and then for fine tuning I compared the GPSDO output to the Rb output on the scope using infinite persistence. Once they are very close it will take a few minutes to see it start drifting either direction. Obviously you can't do this really fast or jitter in the GPSDO itself would mess you up. No matter how much adjustment you do it will always eventually drift with respect to the GPSDO. Ideally I'd like it so that a full cycle of drift took an hour +. Not sure it would last day to day though, in my Temex Rb's you can adjust frequency electronically but also via an analog voltage set by a pot - which will drift some on its own.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on January 04, 2016, 10:38:22 pm
I bought a gpsdo in addition to the symmetricom. From what i can see: Furuno receiver + 8663-xs receiver. Hopefully it artives intact. Update in a few months.
Title: Re: Economical option for precision frequency reference?
Post by: Bryan on January 05, 2016, 09:47:41 am
I did the quick tuning using my frequency counter and then for fine tuning I compared the GPSDO output to the Rb output on the scope using infinite persistence. Once they are very close it will take a few minutes to see it start drifting either direction. Obviously you can't do this really fast or jitter in the GPSDO itself would mess you up. No matter how much adjustment you do it will always eventually drift with respect to the GPSDO. Ideally I'd like it so that a full cycle of drift took an hour +. Not sure it would last day to day though, in my Temex Rb's you can adjust frequency electronically but also via an analog voltage set by a pot - which will drift some on its own.

That is pretty much the procedure that I have done, but with some OCXO's. For the home lab I don't think one can do much better, nor need to. What I do is watch the output of the GPSDO on Lady heather and when I see it at the lowest oscillator fluctuations is when I will do an adjustment. We are talking >+/- 50PPT fluctuations in Lady Heather so think that is about as good as I will get it. If I had a better view of the sky I might be able to get better ADEV readings.



Title: Re: Economical option for precision frequency reference?
Post by: FlyingHacker on March 01, 2016, 07:08:31 pm
How are you using these GPSDOs? Do you leave them up all the time as your lab reference?

Could you simply turn it on, let it warm up and lock, and then calibrate a regular OCXO to it? Then use that regular OCXO as your lab reference frequency?

How accurate a 10MHz do you get with one of these if you only turn it on for a few hours?

My issue is that an OCXO is plenty accurate for a few months, but I need some way to calibrate it periodically. I doubt I can get a GPS signal on a regular basis in my basement hobby lab.

Thoughts?
Title: Re: Economical option for precision frequency reference?
Post by: Macbeth on March 01, 2016, 09:19:16 pm
How are you using these GPSDOs? Do you leave them up all the time as your lab reference?

Could you simply turn it on, let it warm up and lock, and then calibrate a regular OCXO to it? Then use that regular OCXO as your lab reference frequency?

How accurate a 10MHz do you get with one of these if you only turn it on for a few hours?

My issue is that an OCXO is plenty accurate for a few months, but I need some way to calibrate it periodically. I doubt I can get a GPS signal on a regular basis in my basement hobby lab.

Thoughts?
The GPSDO has an OCXO onboard (that it disciplines, hence "Lady Heather" the dominatrix  :-DD ). I don't have any other reference because I am not a time-nut (yet).

Yes, if you turn it off then it will need to re-establish itself, but the 10MHz OCXO will still be available with a good degree of confidence for quite a while during GPS blackouts. That Figure of Merit is available via the serial terminal.

Also, your basement lab shouldn't be a problem as an external active "GPS mouse" is all you need - I have mine attached to a drain pipe outside my window. If you need more than a couple of meters of cable then there are trim factors you can specify to the GPSDO to let it correct for that.
Title: Re: Economical option for precision frequency reference?
Post by: FlyingHacker on March 01, 2016, 10:19:27 pm
Thanks for the reply.

So whenever you turn off the GPSDO do you have to re-establish a GPS lock for it to be accurate again, or is the control voltage stored in some non-volatile medium, allowing it to boot up to the same accuracy as when it shut down?

I guess I am trying to figure out if you need a GPS signal every time you power cycle the unit.

Is this comparable:
http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

I mainly want something to calibrate to.

Thanks.
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on March 01, 2016, 10:39:50 pm
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.
Title: Re: Economical option for precision frequency reference?
Post by: FlyingHacker on March 01, 2016, 11:11:32 pm
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.

I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on March 01, 2016, 11:35:18 pm
I have found my Trimble units to be very good at power on even without a GPS lock. However if you're storing them for several months unpowered I think you'd want to power them on for several hours with a solid GPS lock before using them to calibrate other equipment.

I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)

It's not just a matter of preserving the control voltage in non-volatile memory, it's physical changes to the crystal that happen when it sits powered off - the longer it sits that way, the worse. There's some good info on that on the thread (may be the other thread I started on this topic).  That said, I think all those issues have to do with phase noise, not the overall usefulness of the frequency standard for 99.999% of the use cases.

FWIW, I installed an OCXO in my HP 53131A, but I've since switched over to using the GPSDO. I got a splitter and use it as the external ref for my Siglent function generator as well.


Title: Re: Economical option for precision frequency reference?
Post by: FlyingHacker on March 01, 2016, 11:52:54 pm
I assume they feed a control voltage to the OCXO PLL based on the GPS info. Do you know if that control voltage is stored between boots? Or is power on today the exact same as power on last year? (Rather than the same as the last power off?)

It's not just a matter of preserving the control voltage in non-volatile memory, it's physical changes to the crystal that happen when it sits powered off - the longer it sits that way, the worse. There's some good info on that on the thread (may be the other thread I started on this topic).  That said, I think all those issues have to do with phase noise, not the overall usefulness of the frequency standard for 99.999% of the use cases.

I see. So with the GPS whipping the OCXO into shape it can account for phase noise as well?

I have a 5 port video amp on order. I was going to convert that to 50ohm.

Do you think this eBay item is comparable to the ones you guys use:

http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

EDIT: This seller looks better:
http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263 (http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263)

I see a few out there, and want to make sure I get the "good one."

Thanks!
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on March 02, 2016, 12:10:58 am
I see. So with the GPS whipping the OCXO into shape it can account for phase noise as well?

No, the GPS is very good for long-term stability, but bad for short-term stability. The OCXO is exactly he opposite - very good for short-term stability, but not good for long-term stability. By using the GPS signal to slowly condition the OCXO, we get the best of both worlds.

Also, FWIW, my GPSDO takes about 24 hours to pronounce itself at full quality after being off for a significant amount of time.

I have a 5 port video amp on order. I was going to convert that to 50ohm.

I think a lot of people go that route. I ended up getting the TAPR TADD-1, but only because at the time I was having trouble finding a good used dist. amp on eBay, with the exception of some giant units that were not practical for me.

Do you think this eBay item is comparable to the ones you guys use:

http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/121530825744?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

EDIT: This seller looks better:
http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263 (http://www.ebay.com/itm/10MHZ-Output-Sine-Wave-GPS-Disciplined-Clock-GPSDO-Antenna-Power-Supply-USA/281802105734?_trksid=p2047675.c100011.m1850&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D35851%26meid%3Dbd3ea62677a64cec9b16b74b0a4ecc33%26pid%3D100011%26rk%3D1%26rkt%3D7%26sd%3D281701995263)

I see a few out there, and want to make sure I get the "good one."

There is this guy in China who has made himself a little PCB to which contains the LEDs, a TTL to RS232 converter chip, mount points for the BNC connectors, and a linear regulator. To this board, he attaches various surplus GPSDO boards from various manufacturers, all of which were manufactured for the cell industry. He also has one GPSDO of his own design, which is the one you list. It is actually pretty decent, except that the frequency is very slightly off due to some error in his calculations. I think the RS-232 interface is also a little whacky (or maybe that unit doesn't even have one, I can't recall). Check out this thread for details on all the BG6TBL units:

https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/ (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/)

If you can find the BG7 unit with the STAR4 board inside, which is made by and uses an Oscilloquartz OCXO, that is the one IMHO to get. It's got a sensitive GPS chip, very good OCXO, and with a small mod to swap the RS232 connection inside the BG7TBL box, you can send commands and receive info to/from the internal processor.
https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg722795/#msg722795 (https://www.eevblog.com/forum/testgear/bg7tbl-gpsdo-master-reference/msg722795/#msg722795)
Title: Re: Economical option for precision frequency reference?
Post by: FlyingHacker on March 02, 2016, 12:56:25 am
Yeah, I found the other thread. I don't seem to be able to find one of the STAR4 models. Grrr.... Anyone?
Title: Re: Economical option for precision frequency reference?
Post by: motocoder on March 02, 2016, 01:44:54 am
Yeah, I found the other thread. I don't seem to be able to find one of the STAR4 models. Grrr.... Anyone?

AFAIK, this guy at 168electronics is hording the actual GPSDO inside the BG7TBL wrapper. He does not want to sell them in small quantities.

http://www.168electronics.com/oscilloquartz-star-4-osa-oem-10mhz-gps-clock-p-122.html (http://www.168electronics.com/oscilloquartz-star-4-osa-oem-10mhz-gps-clock-p-122.html)
Title: Re: Economical option for precision frequency reference?
Post by: usagi on March 19, 2016, 03:37:07 pm
some of the 2015-09-17 models are apparently being manufactured with oscilloquartz ocxo's. you should ping the seller to verify if it's a morion or oscilloquartz (if you actually care).

in any case the most important detail is you get a bg7tbl with a ublox gps receiver.
Title: Re: Economical option for precision frequency reference?
Post by: dagg on August 14, 2016, 02:16:43 pm
I have been running my BG7TBL / 2014-12-09 for quite a while now and it is working fine. I have been trying to get it working as a source for an NTP server using the instructions at: http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html (http://www.satsignal.eu/ntp/NTP-on-Windows-serial-port.html)

I cannot get the receiver t change its settings to match the requirements to work at 4800 baud and use only $GPRMC sentences. I am using the u-center software but none of the settings I send take hold. With the default settings the NTP server software does not use the GPS as the clock.

Any suggestions?

You don't need the (coarse gps) time of the gpsdo, only the pps time sync from it if you manage to see that signal on the windows serial port. In linux (raspberry pi 3) that is no problem.

The clue is:

server 127.127.22.0 minpoll 4 maxpoll 4
fudge 127.127.22.0 refid PPS

and get your coarse time in the normal way through an internet time server.

Jan.

Title: Re: Economical option for precision frequency reference?
Post by: Lee on November 01, 2016, 05:04:54 am
I know these units might be a few dollars more than the BG7 units but how come no one has experience with units such as :

Leo Bodnar Unit
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=234 (http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=234)

Nick Sayer
https://www.tindie.com/products/nsayer/gps-disciplined-xcxo/ (https://www.tindie.com/products/nsayer/gps-disciplined-xcxo/)

And I recently discovered a GPSOD by Bob Stewart that looks very promising.
http://ae6rv.com/ (http://ae6rv.com/)

I am very interested in the BG7 GPSDO's but I keep wondering if spending a few dollars for a unit that is a more modern design and has support might be a better investment in the long run. The BG7's seem to be a little bit of crap shoot as to what surplus gps and oscillator are available.

Anyone using any of these units ?

Lee
Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 01, 2016, 05:16:55 am
You can buy surplus Trimble units for less then 60 USD shipped on ebay, tough to beat the performance per dollar.
Title: Re: Economical option for precision frequency reference?
Post by: Vgkid on November 01, 2016, 06:32:13 am
From the Time nuts mailing list, the AE6RV version will be interesting.
Title: Re: Economical option for precision frequency reference?
Post by: Lee on November 02, 2016, 02:29:16 am
You can buy surplus Trimble units for less then 60 USD shipped on ebay, tough to beat the performance per dollar.

Yes but that is not exactly plug n play GPSDO. You are buying a pig in a poke with no idea of the condition or accuracy.
If someone is trying to get a dead-nuts frequency standard and you don't have $1000 of dollars of calibrated test gear and Rubidium standard then that $60 might sounds like a deal but in the long run is it really worth it ?

I love finding a great hamfest bargain as much as the next guy but I wonder if an aging and deaf gps is really a smart move.
This new generation of GPSDO's are small, accurate, have super sensitive receivers and offer firmware updates and human being on available to help with questions.

I guess what I am suggesting is it might be fun to experiment with a bargain gpsdo board but in the long run does it make good sense financially and in regards to accuracy?

For example: You can get a BG7 setup for around $160. From what I gather from the forum they have had a wide range of every changing surplus OCXO's.
No specs, no measurement, no idea of what you will end up with.

But for $200 someone could purchase something like a Nick Sayers GPSDO with documentation, actual measurements/specs and support.

I think what I am trying to get across is to remind people there Price and there is Cost. And the lowest price might not actually be the lowest in cost in the long run.

Title: Re: Economical option for precision frequency reference?
Post by: TheSteve on November 02, 2016, 03:27:16 am
You have valid points, but I don't think it is that much of a crap shoot buying one unless it is physically damaged - and if it is you can get a refund or replacement. The thread title is economical - pretty tough to beat 60 bucks for a Trimble. Of course you can get better/newer but if someone needs one for the lowest cost possible the surplus Trimble wins. They weren't scrapped because of the GPSDO performance, it was because the cellular protocol in the base station they are pulled from is obsolete.

Title: Re: HP 70K / HP 70000 MMS Microwave system Thread
Post by: rickells on February 11, 2018, 10:14:47 pm
hi,

Please note the start of a Thread for the HP 70000 or HP 70K MMS system & modules:
Future discussion hopes to include: Configuration, Use, repair, software, etc... to further understanding.
HP 70004a, HP 70205a & HP 206a Display units + the HP 70001 Mainframe & a host of HP 70xxx modules.
See:
        https://www.eevblog.com/forum/testgear/hp-70khp-70000-modular-measurement-system-thread/msg1420425/#msg1420425 (https://www.eevblog.com/forum/testgear/hp-70khp-70000-modular-measurement-system-thread/msg1420425/#msg1420425)

thank you