Author Topic: Economical option for precision frequency reference?  (Read 122488 times)

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Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #75 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #76 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.
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #77 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.

 

Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #78 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #79 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.
 

Online Vgkid

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Re: Economical option for precision frequency reference?
« Reply #80 on: July 26, 2015, 03:55:38 am »
Do you know what the receiver is inside the gps box?.
If you own any North Hills Electronics gear, message me. L&N Fan
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #81 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      ","                          "
 

Online Shock

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Re: Economical option for precision frequency reference?
« Reply #82 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/
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM       >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #83 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.

« Last Edit: July 26, 2015, 01:11:14 pm by motocoder »
 

Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #84 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #85 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.
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #86 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #87 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/
Link to product on Amazon: 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.

« Last Edit: July 26, 2015, 06:05:32 pm by motocoder »
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #88 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
 
 

Offline johnny_canuck

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Re: Economical option for precision frequency reference?
« Reply #89 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
 

Offline wiss

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Re: Economical option for precision frequency reference?
« Reply #90 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.
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #91 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.
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #92 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #93 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.
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #94 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

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

 
« Last Edit: July 26, 2015, 10:03:59 pm by N8AUM »
 

Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #95 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

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
 


Offline edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #97 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

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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #98 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

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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #99 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?

 


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