[time-nuts] Quick check of a GPS controller oscillator

[Bob kb8tq]

Hi

With any GPSDO (not just the TBolt) you can do some basic checks:
(They are in no particular order)

1) Are there > 6 sats in view at all times, if not, move the antenna
2) Is the unit locked to at least 4 sats at all times, if not, move the antenna.
3) Has the unit completed its survey process? If not, wait for it to complete.
4) Is the EFC > 10% and < 90% of it’s range after an hour on? If not, repair the unit.
5) Has the unit been on for at least 3 days? If not wait. 
6) Does the output look ok on a ’scope? ( it’s volts not milivolts …) if not repair the unit
7) Does the unit show “locked” or something similar? 
8) Is the EFC consistent ( = stable) and not wandering around? If not repair the unit. 
9) Do the sat’s show SNR’s above 40 db? If not, replace the antenna / coax. 
10) Does it read same / same /same compared to your counter’s internal timebase? 
If not, check the counter / repair the GPSDO. 
11) Does the reported ( survey ) location make sense on Google Maps? If not restart
the survey / repair the unit. 

If the unit passes all those checks, it’s a really good bet that you can trust the output. 
It likely is good to < 1 ppb, almost regardless of who made the device. Not every check
will be possible on every GPSDO. The checks assume you have a ’scope and a counter.
They also assume you can talk to the status port on the device. Some readings ( EFC 
range, SNR, may take a bit of research to put into rational units ….). 

======

If all of that sounds like a lot of work (or not complete enough), buy a second ( or third 
or fourth ….) GPSDO. Next get a couple Rb’s …. maybe a Cs or three …. have you 
looked into Masers?  :)

Bob

> On May 5, 2020, at 8:16 PM, Giuseppe Marullo <giuseppe at marullo.it> wrote:
> 
> Hi,
> 
> I have a ProgRock oscillator that generates 10MHz and 125MHz signals. Checking with my Trimble the ProgRock 10MHz signal is consistently below 2.5Hz compared to the Trimble and also the 125MHz is below about 24Hz.
> 
> My setup:
> 
> - Simmetricon time antenna (26dB gain) in clear view
> - about 10m of RG8X cable
> - Trimble GPS (chinese reboxed)
> - Racal Dana 1998 frequency counter with Trimble as time base
> 
> DUT
> - Progrock (https://www.qrp-labs.com/progrock.html) with
> - ovenized oscillator (https://www.qrp-labs.com/ocxokit.html)
> - GPSQ board (https://www.qrp-labs.com/qlg1.html) outside on the balcony, first floor facing south (almost clear view except North of course). connection is made using rs232 cable (about 6m)
> 
> I tested for harmonics on my FT857D and Argo, every odd harmonic the error increase. The radio has high stability but it is not exact for sure. I could test harmonics with my SA but Trimble would be my only reference.
> 
> The question is: how could I be 100% sure that the Trimble frequency is absolutely trustworthy? I have LH and it says oscillator is within 300-1000ppt.
> Is it enough to conclude the frequency is okay and the ProgRock is wrong?
> 
> TIA
> 
> Giuseppe Marullo
> IW2JWW - JN45RQ
> 
> 
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