[time-nuts] Good Phase-noise?

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Wed Feb 28 18:05:38 EST 2007

Larry Gadallah wrote:
> Hello all:
> I considering a do-it-yourself GPSDO, and I started by looking for a
> good OCXO. I have been given a quote for a unit with the following
> phase-noise numbers:
> -120 dBc/Hz at 10 Hz
> -145 dBc/Hz at 100 Hz
> -155 dBc/Hz at 1 kHz
> -160 dBc/Hz at 10 KHz
> -160 dBc/Hz at 100 KHz
> My question is this: Are these good specs? They look pretty good to
> me, quite comparable to the HP 10811 numbers.
> Thanks,

Whilst these phase noise figures are around 20dB or so worse than the 
state of the art, they are adequate.
The short term frequency stability is determined more by the OCXO's 
Allan variance as a function of averaging time.
In particular the Allan variance for averaging times from 1 sec to 1000 
sec or more is significnt.


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