Author Topic: Economical option for precision frequency reference?  (Read 117848 times)

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Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #125 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?
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #126 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.
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #127 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

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.
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #128 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

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.
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #129 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.
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #130 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 ?
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #131 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 :)
 

Offline SoundTech-LG

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Re: Economical option for precision frequency reference?
« Reply #132 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...
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #133 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.
 

Offline evb149

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Re: Economical option for precision frequency reference?
« Reply #134 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!
 

Online edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #135 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
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #136 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/
 

Online edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #137 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 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
 

Offline Shock

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Re: Economical option for precision frequency reference?
« Reply #138 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

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.
Soldering/Rework: Pace ADS200, Pace MBT350
Multimeters: Fluke 87V, 117, 27/FM       >>> WANTED STUFF <<<
Oszilloskopen: Lecroy 9314, Phillips PM3065, Tektronix 2215a, 314
 

Offline Shock

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Re: Economical option for precision frequency reference?
« Reply #139 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.
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 #140 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 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?
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #141 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

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."

« Last Edit: July 30, 2015, 02:08:38 pm by motocoder »
 

Offline motocoder

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Re: Economical option for precision frequency reference?
« Reply #142 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?
 

Offline SoundTech-LG

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Re: Economical option for precision frequency reference?
« Reply #143 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/


 

Offline SoundTech-LG

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Re: Economical option for precision frequency reference?
« Reply #144 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
 

Offline evb149

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Re: Economical option for precision frequency reference?
« Reply #145 on: July 31, 2015, 08:06:37 am »
Thanks for the great information all!
 

Offline N8AUM

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Re: Economical option for precision frequency reference?
« Reply #146 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

 

Offline Shock

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Re: Economical option for precision frequency reference?
« Reply #147 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.
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 #148 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

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.

 

Online edpalmer42

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Re: Economical option for precision frequency reference?
« Reply #149 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
 


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