I am using the PPS from a Garmin GPS16 to timestamp a VLF signal received directly via a PC soundcard. Signal into one channel, PPS into the other.
Using pulse centroid timing, I'm seeing about 0.5uS jitter of the pulse-to-pulse interval, and an exponential moving average with time constant 100 seconds is applied to smooth this out. What I have left is a slow cyclic variation of the signal timestamping. It shows up when I measure the phase of an off-air signal, eg here is MSF 60kHz from Anthorn. http://abelian.org/vlf/live/pp100701msfb.png The same variation appears (in unison) on other off-air timing signals, eg DCF and HBG both show the same cycle, so I guess this is variation of the GPS PPS itself, not the VLF signal phase. The period is about 3000 seconds and the amplitude corresponds to about +/- 1.4uS. Having no prior experience of using GPS PPS timing, I was expecting some pulse-to-pulse jitter, but this slow variation has caught me by surprise. Question: is this typical of GPS timing signals, or have I got a problem in my software? -- Paul Nicholson http://abelian.org -- _______________________________________________ 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.
