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

[Matthias Welwarsky]

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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