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. -------------------------- How long did you run your tests? _______________________________________________ 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.
