Hi Most modern receivers give you corrections in ps rather than ns. That's not to say they are *good* to 1 ps. It's not uncommon to see adev (after doing the correction) running sub 1 ns at one second when compared to a 5071.
Most people seem to do this in runs many minutes long. That's a bit away from 1 second, so other things do come into the picture. Bob On Apr 16, 2013, at 3:42 AM, "Tom Van Baak" <[email protected]> wrote: >> 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 -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
