[time-nuts] How to measure Allan Deviation?

Tim Shoppa shoppa at trailing-edge.com
Sun Oct 22 20:40:30 EDT 2006

Dr Bruce Griffiths <bruce.griffiths at xtra.co.nz> wrote:
> Most GPS receivers with higher frequency outputs than 1Hz, phase 
> modulate the high frequency output in this way and the datasheets 
> explicitly indicate this.
> Thus there would appear to be little advantage in phase locking to the 
> 10KHz signal with a short loop time constant.
> To be absolutely sure you will need to use an oscilloscope to observe 
> the synchronous jitter in the 10KHz waveform.

The jitter from the "phase jerked" 10kHz would be in the several to
tens of ns range, once a second, right?

Period of 10kHz is 1E5 ns.

I don't think I can trust my old analog scopes to do this, but a
fancy coincident trigger (require coincidence with PPS)
on a digital storage scope with a crystal timebase might see this.
Sounds more like a job for histogramming interval measuremnts.
(In my lab days we did this with a TAC followed by a PHA for
much larger scale jitter measurements).


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