[time-nuts] 5061 Cs frequency shift with long time constant?
John Ackermann N8UR
jra at febo.com
Tue Apr 5 19:41:37 EDT 2005
Thanks, Brian. That's very helpful. I looked at the schematic and the
cap they are using for LTC is 8uF that's simply put between the input
and the output of the op amp module.
I guess the question is whether the leakage causes any stability
problems, or just a constant offset. Time for some experiments...
John
----
wa1zms at att.net wrote:
>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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