[time-nuts] Segal law: freq difference for GPSDO

Vlad time at patoka.org
Wed Mar 30 01:04:54 EDT 2016



>> May be somebody could recognize, what 10.0000014 Mhz could be used for 
>> ?
> 
> It sort of looks more like an unlocked OCXO than a magic frequency.
> Measure phase instead of frequency; see how the phase drifts over time.
> Also check if the magic frequency varies or drifts over time.
> See if the offset is constant in spite of a one hour power cycle of
> either GPSDO.


To feed my curiosity, I disassembled Starloc II to have a look what is 
inside. There is Motorola GPS module and DATUM OCXO.
I measured 5V ref (stamped on PCB). Its looks good. The OCXO has 12V on 
its VSS pin. No visible damage there.
I put it back. I think its possible to replace DATUM OCXO by Morion. The 
pinout and voltage is the same. Moruib is slightly bigger in size, but 
should feet the case with minor modifications. However I postpone this 
exercise for now.

I don't have "native" software to manage StarLoc. But since its TSIP and 
I was using TB Monitor to see some information.

Here is how its looks like:

https://www.patoka.ca/OCXO/TBvsSL/StarLocIImonitor.png


Also there is series of screenshot from my Oscilloscope where I tried to 
compare 1PPS outputs


https://www.patoka.ca/OCXO/TBvsSL/

> 
> The TBolt/LH screen seems ok. Send some RS232 commands to the StarLoc.
> Verify they are both receiving a good number of SV, and maybe even a
> lot of the same set of SVN.

I am not sure if StarLoc is responsive for any commands. I need to dig 
it little more.

> You can also remove the antenna on one or both units. See if the
> unusual frequency offset and the ADEV curve looks the same with or
> without antenna.

Thanks for the advise !


-- 
WBW,

V.P.


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