[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:
> 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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