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

Tom Van Baak tvb at LeapSecond.com
Sun Jul 7 16:06:41 EDT 2013


Hi Bob,

Send me the raw data and I'll have a look to confirm or explain your results.

I've seen this in some of my FTS 1050 also; it's always been the fault of the battery charger circuit.

/tvb

----- Original Message ----- 
From: "Robert Darby" <bobdarby at triad.rr.com>
To: <time-nuts at febo.com>
Sent: Sunday, July 07, 2013 12:27 PM
Subject: [time-nuts] Question about effect of sample interval on ADEV


> 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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