[time-nuts] Question about effect of sample interval on ADEV

Robert Darby bobdarby at triad.rr.com
Sun Jul 7 15:27:16 EDT 2013


This is a question that has probably been addressed on the list and in 
various texts but I've been unable to find an answer that I can fathom 
so here's a request for some info about the behavior of TimeLab (and 
probably all other similar programs).

I have been trying to find the source of some periodic noise that 
appears when using a 5370B to measure an FTS 1050B against a 5065B.  The 
noise manifests itself varying from 12s to 20s in a repetitive fashion.  
I asked C. Dawson about this and one of his suggestions was to try a 
longer sampling period.  Down the rabbit hole I went!

I ran four trials in succession at sample intervals of .07s, .25s, .5s, 
and 1s.  The result is as if the adev ,modified, and Hadamard curves 
have been slid down and to the right along the noise floor of the 5370.

My assumption, apparently incorrect, was that the software would take 
the sampling interval into account so that I would get essentially the 
same plot. When I edit a plot changing the sample interval, the trace 
remains essentially unchanged and this seems inconsistent with the 
results noted above. Can anyone explain in relatively simple terms what 
I'm missing?

Thanks,
Bob Darby



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