[time-nuts] Some GPSDO measurements with an upgraded 53131A

[Matthias Welwarsky]

Hi,

decided to follow up with a little sanity check: I pitted my DiY attempt 
against a "commercial" GPSDO, a Trimble branded UCCM, sourced from Ebay. Of 
course I have no idea whether the Trimble still meets specs, or what these 
specs even are, but I think all in all I'm doing not so badly with my own 
design.

I logged two traces of the Trimble, one with the 53131A in frequency mode, one 
with a TAPR TICC in timestamp mode. Reference again the upgraded timebase of 
the 53131A.

See the attached graphs.

BR,
Matthias

On Mittwoch, 15. Juli 2020 18:33:08 CEST Matthias Welwarsky wrote:
> Dear all,
> 
> I recently acquired a 53131A counter and upgraded it with an OXCO timebase.
> I decided to test it out a bit to see what results I could be expecting
> from it.
> 
> So I hooked up two of my DiY GPSDOs to hopefully get some actual data
> instead of running DAC value series through MDEV and wondering what the
> graphs might mean in real-world terms. I chose a fairly simple setup, just
> logging frequency data with a 2 second gate time as this would give me
> another digit of output.
> 
> For lack of a better option, I decided to use the internal timebase of the
> counter, which is now a used MV89A OCXO I bought on Ebay.
> 
> Attached find the resulting MDEV graphs. It looks like I can actually "see"
> the "BBB GPSDO", which is a GPSDO cape I'm currently developing for the
> Beaglebone Black. It's equipped with an ebay'd MV85A OCXO and a Ublox M8T.
> 
> The second trace is my Rb-GPSDO which uses a LPRO-101 as the LO. I think I
> can safely say that this one is down in the measurement noise. Only beyond
> the 1000s mark it might be visible, but this is also the point where the
> drift of the counters timebase starts to dominate the graph. At best this
> graph can serve as a baseline for the counter.
> 
> Both traces have frequency offset and linear drift removed.
> 
> BR,
> Matthias

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