[time-nuts] Re time-nuts Question about effect of spurious frequency modulation on Allan Deviation

Henk Peek henkp at nikhef.nl
Tue Aug 7 06:24:15 EDT 2018

On Monday, August 6, 2018 07:12 CEST, "Richard (Rick) Karlquist" <richard at karlquist.com> wrote: 
> I need to measure ADEV on a source that has spurious
> sine wave frequency modulation on it.  I am looking for a
> formula that would tell me ADEV, vs FM deviation and
> carrier frequency. I'm not sure if modulation frequency
> or tau matter.  I am hoping to determine how much
> I need to clean up the signal order to get down to a particular
> ADEV measurement threshold.

Use an ADEV sample period of the FM modulation frequency period
or sub-harmonic period. This samples the frequency modulated signal
at a constant phase of the modulation and generate notches at the 
FM modulation side-bands of the ADEV samples.
Result: the ADEV samples don't contain the FM modulation.

Henk Peek 

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