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

Mike S mikes at flatsurface.com
Tue Jul 12 17:16:27 UTC 2011

At 08:01 AM 7/12/2011, Michael Eder wrote...
>For our buoy deployments we have GPS and a highly accurate oscillator
>conditioned by the GPS PPS.  Unfortunately when we let this run for 
>periods we see both the GPS and PPS being marked as false tickers....
>I did try setting minclock and minsane, to two and one respectively, 
>this did not seem to change the situation.

Try adding "tos mindist 0.015" to your ntp.conf. This widens the 
correctness interval used by the clock selection algorithm. Basically, 
it accommodates the jitter in the serial NMEA stream. 0.01 is another 
commonly used value, but you may want more or less. It should be as 
small as possible while providing reliable operation.

 From the docs ( http://www.cis.udel.edu/~mills/ntp/html/prefer.html ):
"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." 

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