[time-nuts] GPS message jitter (preliminary results)

[Mark Sims]

That plot was from a 12 hour run.   I've done 48+ hour runs and did not see anything strange.   I'm not currently measuring the offset of the message from the 1PPS,  just the stability/jitter in the timings of the last byte of the timing message.   If the timing message offset time from 1PPS jumped, it would show up as a spike in the message jitter (and if the offset jump was not particularly large, would be hidden in the normal noise of the end-of-timing-message time stamps.   

Adding the message jitter measurements to Lady Heather was a quick and dirty 5 line code hack to investigate whether one needed a 1PPS signal to usefully drive a clock display.  So far it looks like you could easily get +/- 30 msec stability from a cheap GPS without the 1PPS (and much better with some software averaging)... and that is on a non-real-time, multi-tasking operating system going through who knows how many layers of serial port message buffering, etc.  Using a dedicated micro to do the deed should be quite a bit better.  You should, of course,  measure and compensate for your chosen receiver's message offset time to the 1PPS to get an accurate time display.

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How long did you run your tests?