[ntp:questions] Loop Filter Gains vs. Polling Interval

David Woolley david at ex.djwhome.demon.invalid
Mon May 16 07:01:12 UTC 2011


Mischanko, Edward T wrote:
> Can anyone tell me, does the sensitivity for frequency adjustment lessen
> as the polling interval increases?  I ask because I'm observing that my

They are linked, but I have a feeling that the loop time constant is not 
clamped, even though the poll interval is.  The aim is to always achieve 
a certain level of oversampling.  At the very least, the intent is to 
vary the time constant and then choose a poll interval that is 
appropriate for that.

> offset increases and the frequency adjustment decreases to the point I
> fall out of sync at polling intervals above 256.  What am I doing wrong?

The integral component should be retained.  The effect of having too 
long a loop time constant should be that the system fails to track clock 
wander, so would be more vulnerable to temperature changes or forgetting 
to disable power management of clock frequency.




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