[time-nuts] Thunderbolt Loop Damping

Tom Van Baak tvb at LeapSecond.com
Tue Jul 8 14:34:18 EDT 2008


> As far as what the statistics are showing... well they show
> the ADEV values of the Thunderbolt's own measurements
> of the signal errors (auto ADEV?).  How those compare to
> measurements against an external reference is left as an
> exercise to the reader.  

What you're calculating is the combined ADEV of the GPS
ref, the internal measurement system, including internal any
filtering, and the OCXO. Your numbers can't show GPS, or
the measurement system, or the OCXO by themselves, nor
do your numbers reflect the actual GPSDO output signal
performance as compared to a real reference clock. That's
why it sort of looks like what you have left "as an exercise
to the reader" is pretty much the entire exercise.

Do have access to a Rb that you can use as a reference?
Send me email offline if you'd like to borrow one.

Still, one thing you could do now is see the effect of varying
the loop time constant. With a tight loop the sdev or adev of
TI and ppb will be very small; the looser the loop the wider the
variance of those values. That's my guess at least.

/tvb





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