Hello David, I trust the clock, because with constant temperature crystals perform pretty good. The clock is disciplined with PPS, but no adjustments happened during the measurement, so it runs with a constant frequency offset. It took a few days to reach that state.
My point is that NMEA on this device does not jitter with a gauss distribution or similar, but in a way that causes the reasonable jitter calculation to give too low values. The jitter diagram shows why 0.1 as minimum distance suffices. The problem is, that this is only a workaround, as it effects the root dispersion. What I need is to bypass the NMEA jitter calculation only, or give a minimal value for that, to prevent it becoming a false ticker when the actual jitter is larger than the estimated jitter. In the diagrams that happens if the estimated jitter does not cover zero, because zero is the PPS/crystal clock with 4 us jitter (both estimated and actual). GPS reception was fine with good average SNR and a reasonable of used and visible satellites. TDOP was fine. I had this behavior before the upgrade from firmware 4.00 to 4.20, which is recommended due to the GPS week rollover. I did not have it when the GPS reception was worse and I had a lower average SNR and an overall higher NMEA jitter and worse TDOP. Michael _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
