[time-nuts] Plot phase noise spectrum from DMTD measurement?

Stephan Sandenbergh ssandenbergh at gmail.com
Tue Mar 8 18:46:05 UTC 2011


Hi,

I recently noticed something interesting: The DMTD measurement gives a set
of phase values x(t). From which fractional frequency y(t) is calculable. So
now it seems viable to plot the spectrum, Sy(f) and if you scale it properly
you arrive at Sphi(f). If I'm  not making a gross error somewhere the math
seems to check out. But, I'm wondering is there a physical reason why this
isn't valid?

I have not seen this being done anywhere - so I assume there is. However, it
seems possible to plot Sphi(f) for 1Hz < f <100kHz when having a vbeat =
100kHz sampled for 1 second.

I'm familiar with the loose and tight phase-locked methods of measuring
phase noise, but am quite curious to know if phase noise from a DMTD
measurement is a valid assumption.

I would guess that if the frequency domain phase noise measurement requires
phase-lock then the time-domain measurement requires as well. However, here
in lies my real interest - two GPSDOs are phase-locked (not to 1Hz,
something far less I know) so can it be possible to measure GPSDO Adev and
phase-noise using a single DMTD run? Am I making a wrong assumption
somewhere?

Cheers,

Stephan.


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