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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