[ntp:questions] Maximum time2 fudge value for NMEA refclock?

David J Taylor david-taylor at blueyonder.co.uk.invalid
Tue Jul 20 11:30:20 UTC 2010

"Rhys" <user at mailinator.org> wrote in message 
news:MPG.26b018b8126a17a1989681 at news.optusnet.com.au...
> Sorry I should have said, GPS18x. Now that its stabilised its still 20-
> 80ms positive out in ntpq, so either my offset didn't actually change,
> or in the wrong direction.

For NMEA alone, no PPS, you may get poorer performance then just with 
LAN/Internet sync.  Just to remind me, you're somehow measuring one system 
against another?

> Seems a regular thing for it to jump crazy on startup, makes fine tuning
> a little impossible. PPS takes 30 minutes i think to reappear, it might
> be kernal PPSing in the background vs NTP trying to synch to NMEA.

What do you mean "reappear"?  To be present on ntpq -p at all, or to have 
the synced tag "o"?

> I was thinking about turning on more NMEA sentences to see if it
> stabilises NMEA, but getting to the Windows boot on that isn't easy now,
> and this main PC has no serial.

I would have thought that the fewer sentences the better, to be honest, 
although I've seen one recommendation to use the sentences which include 
the number of satellites locked (IIRC) so that you can get a measure of 
how marginal GPS lock might be.

My own tests showed that while a serial-to-USB converter made accuracy a 
lot worse, it could still be better than a LAN connection alone.



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