[ntp:questions] NMEA ref.clock better than my ISP's timeserver?

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Thu Jun 11 16:28:12 UTC 2009


David Lord wrote:
[]
> I only have a pair of servers as peer and that is maxpoll 8 and
> both sat at 256 sec. Offsets are 203us and 593us.

I see more like 1-3ms for the Internet servers (compared to the GPS), with 
delays in the order of 30ms.  This is with Windows, though, not a UNIX 
system.

> I have problems with the larger maxpoll value as temperature
> changes are sometimes at a higher rate than ntpd can compensate
> for but this affects the pcs differently and having peers with
> lower maxpoll might help. Otherwise the higher maxpoll does
> seem to tend to give lower offset variation and jitter. So far
> this year I've not had temperature in back room shoot from 15C
> to near 30C as happened on a couple of days last year.
>
> David

Yes, it's the classic trade-off - high precision requires a long 
time-constant, but that means a poorer response to temperature changes. 
You have to decide when you have it "good enough", otherwise you will be 
tinkering for life!

Cheers,
David 




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