[time-nuts] How to measure Allan Deviation?

Didier Juges didier at cox.net
Sun Oct 22 21:25:34 EDT 2006

Dr Bruce Griffiths wrote:
> In principle this measurement could be made with a time interval counter:
> delayed 10KHz -> STOP
> Vary the delay and watch the jitter jump when the leading edge of the 
> PPS signal occurs during the 10KHz burst which was phase coherent with 
> the previous PPS pulse.
> The only problem is finding a suitable variable delay device with 
> sufficiently low (<=1ns??) jitter.
The delay device can be triggered by the 1 PPS, then will drive the ARM 
input of the counter, so as long as the delay device's jitter  is less 
than the 10 kHz period, if we adjust the delay to 0.99985 second 
(between the last 2 periods of 10 kHz before the 1 PPS), then the TI 
counter will START on the last 10 kHz pulse before the pps, and STOP on 
the 1 PPS.
Tek has some time delay generators in the TM-500 and 7000 plug-in 
series. I knew one day I would need one of those, I now know why :-)


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