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

Bill Hawkins bill at iaxs.net
Wed Apr 6 16:28:21 EDT 2005

Perhaps there is nothing wrong with the integrator. The control
voltage is brought out to a jack. Granted you have nothing that
can measure volts to 10E-12 or 13, but do you see a change in
voltage when you switch from 100 seconds to 1 second time constant?
You should wait ten time constants or more after switching. Wait,
that's just a rule of thumb. How many time constants do you have
to wait to get a time constant delta below 10E-13? My Burrington's
tables don't go to that accuracy.

Perhaps the 1 second time constant is required for tight control.

Bill Hawkins

-----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 8:53 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 



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 

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