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[time-freq] Frequency Standards - Which to believe?

Arthur Shulman dentist at nornet.on.ca
Sun Jul 2 01:14:20 UTC 2006


Directed to Eric & Alberto who were kind enough to answer my question, this is
the result:

Following the advice of both gentlemen, which was essentially the same, I
proceeded to access the C-Field adjustment on the Rubidium standard, and with
some care and experimentation, was able to adjust the period of disagreement
(one complete Lissajou cycle) to about five minutes. This adjustment was very
broad and repeatable, but I thought I might be able to do better.

I next took the outputs of both standards and read the phase difference at 10
mhz with an HP8405A Vector Voltmeter. It was necessary to use the appropriate HP
attenuators to avoid damaging the voltmeter sampling probes. This indeed was a
sensitive and stable indicator, and it quickly became apparent that much
improvement was possible!

I monitored the phase difference for about a day, and finally stopped adjusting
when it seemed to me that I could no longer tell which standard was getting out
of phase, the Rubidium, or the GPS one! At this point, I estimated that that the
period for one complete 360 phase shift was in excess of 45 minutes, and
probably actually exceeded an hour!

Taking refuge in deference to the Law of Diminishing Returns, I buttoned up both
standards and put them into service!

Thank again for your assistance!






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