[ntp:questions] Loop Frequency and Offset

Miguel Gonçalves mail at miguelgoncalves.com
Tue Sep 27 10:29:31 UTC 2011

On 27 September 2011 01:29, unruh <unruh at wormhole.physics.ubc.ca> wrote:

> Any(?) gps receiver which has PPS output does better than 1us.  Any
> network does much worse than 1 us ( more like 10s of us to hundreds).

I might be wrong but checking for instance the Garmin 18 LVC specifications
(http://www8.garmin.com/products/gps18oem/spec.html) I do not see better
than 1 us accuracy.

> > I know... :-) My cable connection is really bad for NTP... I can't get
> > better than 3 us. That is why I have 2 stratum 1 GPS receivers onsite.
> You will NOT bet 3us from any network connection.
> Are you sure you are not confusing microseconds (us) with milliseconds
> (ms)?

I don't mix ms and us... I wasn't BETTING on anything... :-) It was a typo
of course (errare humanum est).

> And even with a high accuracy timing receiver you will not get better
> than ab out 1us because of hardware interrupt latencies and variability,
> etc (and thermal wandering of your computer clock) unless you have some
> very specialised hardware.

1 us is OK for me.


More information about the questions mailing list