Thread: Homebrew GPSDO
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Old 6th Mar 2021, 7:21 am   #15
mole42uk's Avatar
Join Date: Aug 2010
Location: Bristol, UK
Posts: 2,142
Default Re: Homebrew GPSDO

Originally Posted by Radio1950 View Post
If there is any doubt, if there is any slow circle wander, even very slow, there is a problem, and you have to rethink the process.
A GPSDO with an output frequency within a few Hz of nominal is not operating correctly.
This is my current dilemma. The lissajous test gives me a wandering circle so I know that one of the references is not accurate. The one I borrowed is a commercial unit based on a Trimble core so Iím inclined to trust that.

Investigating my DIY version, I have no confidence that the GPS 10kHz is having any effect on the OCXO. Fiddling with the resistors in the feedback circuit gets me to about 2 phases per second but it not locked, removing the antenna from the GPS (which should disturb it enough to be measurable) doesnít make any difference.

I believe that I should be able to get two GPSDO to give me a perfect lissajous circle after they have settled - but these have both been running in the bench now for a week.

recursive loop: see recursive loop
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