[time-nuts] Fluke PM6681 'fault' or 'characteristic'?

Magnus Danielson magnus at rubidium.dyndns.org
Tue May 30 08:56:22 EDT 2017

Hi Ed,

Looks kind of reasonable. Signal level and slow phase-drift can 
illustrate some interesting properties which is sometimes hidden.

You have cross-talk and that can interact in interesting ways. You 
mention low signal levels, and well, this would be consistent with that.

You should square the signal up using gain, stage. See the Wentzel 
approach, as being used at the clock input of the TAPR TADD-2 for instance.


On 05/30/2017 04:54 AM, Ed Palmer wrote:
> I was comparing my Sulzer 2.5 to my Efratom FRT and saw something very
> odd.  I don't know if my PM6681 has developed a fault or if I'm just
> measuring two oscillators that are good enought to show oddities in my
> measurement system.
> When the phase of the two signals drifts through zero, the measurement
> gets noisy.  The levels are very low as you can see in the attached
> graph.  Without the averaging, you can barely see anything.  But the
> degradation is significant.
> I've checked my counter and can't find anything wrong.  Power supplies
> are clean.  I've worked through the voltage tests and adjustments in the
> service manual.  Nothing was out of adjustment and nothing improved.
> Does this look like a fault or is it just another reason to avoid phase
> wraps and the dead zone around zero degrees?
> Thanks,
> Ed
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