[time-nuts] How can one measure ADEV of a good oscillator?
Dr. David Kirkby (Kirkby Microwave Ltd)
drkirkby at kirkbymicrowave.co.uk
Mon Dec 1 02:09:14 EST 2014
I think I have a flaw in my understanding of this.
How can something like an SR620 measure the ADEV of an oscillator, if the
oscillator is of a similar or better than the reference fed into the SR620?
I see plots of ADEV for hydrogen masers, but I can't understand how this
can be measured from the phase data unless the reference is better than the
DUT, which is not going to be possible with a good hydrogen maser.
I was thinking it might be possible if one has 3 oscillators and 3 time
interval counters to perhaps solve 3 simultaneous equations. I can't prove
that, but it seems intuitively correct.
I must be missing something!
Also I have seen graphs of both Allan variance and Allen deviation. Both
are typically 10^-12 for a decent oscillator, but given the variance and
standard deviation are related by a square root, they can't both be around
10^-12. I would expect to see values of 10^-6 or 10^-24, but I don't see
such dramatic differences from 10^-12.
If I see numbers around 10^-12 on an OCXO, is that the Allen variance or
Allen Deviation?
Dave
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