[time-nuts] 5061 Cs frequency shift with long time constant?

[wa1zms at att.net]

John-

I have seen the same effect on my HP-5060A.  I had attribute it to
leakage in the loop filter capacitor.

Should you find that you need to replace that cap in your standard,
you might want to try some of the very low leakage current caps from
WIMA in Germany.  If you're in a pinch I have a couple 1uF WIMA caps
that I could send you.

-Brian, WA1ZMS

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of John Ackermann N8UR
Sent: Tuesday, April 05, 2005 9:53 AM
To: Discussion of precise time and frequency measurement
Subject: [time-nuts] 5061 Cs frequency shift with long time constant?


This is very odd (I seem to be collecting these sorts of problems) and I 
wonder if anyone else has seen something similar.

I got my 5061A trimmed to the point where a 5 day run against GPS showed 
an offset of less than 1x10e-13.  I then switched the unit into the long 
time constant mode and now see that the offset (over 36 hours) is 
-1.7x10e-12.  Nothing else in the setup has changed.

It's hard for me to see how simply changing the loop time constant would 
change the frequency of the standard, especially by this much, but 
stranger things have happened.

Has anyone else experienced a shift like this when switching the time 
constant?

Thanks,

John

PS -- I was able to partially, but not completely, reproduce the phase 
shift that I wrote about a couple of weeks ago by jiggling the 1 PPS 
cable to the counter.  Replacing that cable seems to have resolved that 
problem.

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