[time-nuts] FTS4060 C Field Time Constant

John Ackermann N8UR jra at febo.com
Thu Feb 17 16:57:27 EST 2005

Brooke, I've been seeing something similar myself.  Last weekend I 
posted a message with an attached plot vs GPS that showed similar 
behaviour with a significant change in slope a couple of days after 
changing the C field.  And, I lost the green "continuous operation" 
light at the time of the change (I was running with the long 60 second 
time constant, which will knock out of lock very easily).

A new plot (check 
http://www.febo.com/time-freq/plots/hp5061a-n8ur_1.html) against the 
quieter of my two Z3801As is showing better behaviour now that the last 
C field adjustment is over a week ago, but even there it appears there's 
an initial downward slope that levels out.


Brooke Clarke wrote:
> Hi:
> In still in the process of setting the C field on my FTS-4060 and have 
> an interesting observation.  After a cockpit error where I made a change 
> in the wrong direction the time interval plot was going up steeply.  In 
> line with my latest theory of how to make the adjustment (which is to do 
> a binary search rather than try and compute the required adjustment) I 
> then set in a new value.  I thought I saw a time constant of about 3 
> hours (i.e. it took about 3 hours to get to 63% of what I thought was 
> the final value). 
> The next day (24 hours later) for about 8 hours the time interval was 
> constant to within 10 nano seconds, phenomenally stable operation.
> Now 3 days after that I can see that the time interval has a down 
> slope.    So the very stable operation 24 hours after the C field change 
> was during the time when the frequency was changing and was at the level 
> part of the curve.
> This indicates that for a C field change on the FTS4060 you need to wait 
> at least 2 or 3 days before making any measurements! 
> This also may explain why trying to compute the amount of a change does 
> not seem to work.  This would be the case if the effect of the prior 
> change had not yet settled in.
> Have Fun,
> Brooke Clarke, N6GCE

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