[time-nuts] FTS4060 C Field Time Constant
Brooke Clarke
brooke at pacific.net
Thu Feb 17 17:06:58 EST 2005
Hi John:
The only reason I saw this was because the plot had a steep positive
slope, then 24 hours later appeared to be perfect, now a few days after
that obviously has a negative slope. My initial estimate of the time
constant, based on the perfect performance, of 1 tau = 3 hours, was way
off. The real tau is more like 1 day. So I'll wait another day before
making the next adjustment.
Do you have plots that cover longer time periods?
Have Fun,
Brooke
John Ackermann N8UR wrote:
> 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.
>
> John
> ----
>
> 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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