[time-nuts] OCXO Phase Noise Measurement in Primitive Conditions
phk at phk.freebsd.dk
Wed Aug 27 13:32:27 EDT 2014
In message <1409158879.13035.YahooMailNeo at web142706.mail.bf1.yahoo.com>, Bob St
So here is a pretty interesting way to optimize a GPSDO that I've
been playing with for some years. I don't have a formal mathematical
formulation of it.
It is somewhat related to what Dave Mills calls "the Allan intercept"
except this you can actually measure and not just estimate.
You run several (long!) test-series with different timeconstants
in your PLL, and you record the resultant EFC and phase offset
as a function of time.
If your timeconstant is too short, you will have a lot of
high-frequency signal in the EFC, too long and you get too
much high-frequency signal in the phase offset.
The optimal timeconstant is where you have the least sum of
spectral power where the two curves cross each other.
My experience so far is that the curve around the optimum is
very flat, getting the timeconstant wrong by a factor of two
hardly changes the resultant performance.
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