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

[Richard (Rick) Karlquist]

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.

I tried a literature search but didn't turn up anything
I could use.

I remember when I worked on the output section of the 5071A
we specified 100 kHz and 1 MHz spurs to be down -80 dBc.
These didn't seem to affect the ADEV of the 10 MHz outputs,
but I can't prove why this should be the case.  Does the
f-sub-h measurement bandwidth come into play?

Thanks.

Rick Karlquist N6RK