[ntp:questions] NTP with GPS and RTC

David Taylor david-taylor at blueyonder.co.uk.invalid
Sat Apr 27 13:56:15 UTC 2013

On 27/04/2013 09:13, David Woolley wrote:
> If the time error is low and bounded the frequency error does not
> necessarily have a low error bound.  Simply polling fast and using a
> short loop time constant can give you a low error bound on the time, if
> the network delays are stable and the source is good.

Thanks, David.  I just checked a power-down reboot of a Windows PC (for 
replacement of a faulty card) with a PPS reference source, and the 
jitter was down to its normal value within 20 minutes, and the offset 
within 15 minutes.  It was much more difficult to judge the time for the 
frequency to stabilise, because there is so much variation with 
temperature - perhaps it took 2 to 2.5 hours.  Certainly not then 10 
hours Bill has often stated.

Another warm PC which had a reboot this morning showed a 12 minute 
jitter recovery time, 3 minutes for the offset to recover (about 50 
microseconds typical) and you couldn't see any step in the frequency graph.
Web: http://www.satsignal.eu

More information about the questions mailing list