[time-nuts] Measuring frequency difference

John Green wpxs472 at gmail.com
Sun Feb 7 18:49:02 UTC 2010

I started out using an oscilloscope and comparing OCXOs to my Z3801 GPSDO.
Later I used it to compare an LPRO 101 to the Z3801 and finally, a TBOLT. I
later acquired a Racal 1992 which makes things a little easier but no more
accurate in my opinion. If you are looking at frequency difference or
frequency drift, and not stability, either of these methods and a stopwatch
will get pretty good results. It took me a couple of days to get an LPRO
adjusted so that I saw one cycle slip every few hours. It takes patience.
The thing that surprised me was how much a TBOLT moved around compared to my
Z3801. Though it stayed within one cycle because it was "phase locked", it
jumped around a good bit while the LPRO just slowly slipped in one direction
or the other.

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