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

[Ed Palmer]

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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