> I wonder if one should only measure the PPS thought. Looking directly at > the clock could help to separate the clock drift and the time, even if > you get sufficient clues from the PPS and sawtooth correction. > > Cheers, > Magnus
I've never tried that. Start with checking the ADEV of the LO. I always assumed the 1PPS was pre-compensated for instantaneous LO offset and rate, as calculated during the previous second(s). If so and ADEV(1 s) is less than 1e-9 then the 1PPS + sawtooth will have sufficient accuracy for your needs. Message @@Ha contains the oscillator and clock parameters. As you know professional receivers bypass this issue because they take an external LO (e.g., Rb, Cs, HM). When you look at the actual clock solutions (which are in the @@Hn message) you will be surprised at the variance. At the per-SV per-second level it is not uncommon to see errors of many ns, even tens of ns. But when you average up to 12 SV together every second for 600 seconds then you start to see something trustable. You can see first hand why GPSDO need long time-constants. Here's a one second sample of a single Hn message: @@Hn: sigma 36 sawtooth 10 0 0 00000000 mean frac 861564.000 (0.000) ch 0 sv 6 frac 0.000861576 s = mean + 12 ns ch 1 sv 5 frac 0.000861586 s = mean + 22 ns ch 2 sv 10 frac 0.000861581 s = mean + 17 ns ch 3 sv 19 frac 0.000861573 s = mean + 9 ns ch 5 sv 13 frac 0.000861571 s = mean + 7 ns ch 6 sv 26 frac 0.000019831 ch 7 sv 28 frac 0.000861555 s = mean + -8 ns ch 8 sv 7 frac 0.000861548 s = mean + -15 ns ch 9 sv 3 frac 0.000861571 s = mean + 7 ns ch 10 sv 8 frac 0.000861546 s = mean + -17 ns /tvb _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
