[ntp:questions] Strange jumps in PPM

mike cook michael.cook at sfr.fr
Wed Aug 21 06:33:40 UTC 2013

Le 21 août 2013 à 08:03, A C a écrit :

> Ok, so I saw the below event in the loops on my system which is controled by ATOM, SHM, and several internet servers.
> I suspect it has to do with the GPS PPS output glitching during extreme satellite events (bad constellation arrangement, fringe signal, etc.)
> Is there a way to have ntpd ignore the PPS quickly if it spins out of control?  The system recovers fairly quickly and the clock doesn't go too far out but it would be nice to avoid these jumps.

 This symptom is common where a receiver's antenna is not well placed. I suspect that you do not have a 360° sky view and probably obstructions or reflecting objects ( buildings etc) in the signal paths. 
 If that is the case and you can get a better antenna placement, that might fix it. I think modern receivers are better at excluding multi-path signals as I have worse results with a UT+ or VP than with a newer one. 

Another possibility would be to profile your horizon and configure the satellites used dynamically, selecting only those  with direct LOS.

 If you have a good uninterrupted sky view, maybe its something else.

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