[ntp:questions] Single GPS/PPS time source gets marked as a falseticker

Mike S mikes at flatsurface.com
Tue Jul 12 18:04:15 UTC 2011

At 01:24 PM 7/12/2011, Chris Albertson wrote...
>On Tue, Jul 12, 2011 at 10:16 AM, Mike S <mikes at flatsurface.com> 
> > At 08:01 AM 7/12/2011, Michael Eder wrote...
> > Try adding "tos mindist 0.015" to your ntp.conf. This widens the
>The above is technically correct but if you find that Internet pool
>servers are seriously out performing your GPS, then maybe you need a
>better GPS.

Your're misunderstanding the problem. NTP won't use the 
much-better-than-Internet PPS signal without an associated clock which 
delivers TOD. My understanding is that the mindist ensures that the 
serial (NMEA) time source, the "prefer" peer, isn't set to falseticker 
due to high jitter (which would make the associated PPS source one, 
too.) As I already cited and quoted: "the prefer peer can still be 
discarded by the intersection algorithm as a falseticker. To avoid 
this, it is usually wise to increase the mindist option of the tos 
command from the default .005 s to something like .05 s."

So, a pool server may be outperforming the serial TOD source, but it's 
not outperforming a reasonable PPS source, so there isn't a problem. 
The solution is correct practically and technically. 

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