On Mar 9, 8:02 pm, jack <[email protected]> wrote: > > I am trying to sync my Windows box to an external GPS source. I > currently have BU353, whose output is not very periodic. I read up on > ntpd implementation that uses PPS signal but I don't even have an RS > 232 port on my computer.
Google tells me that's a USB GPS mouse. > My questions: > 1) what's the best GPS antenna (and protocol) in terms of > consistencies in its output? > 2) what kind of accuracy can i expect? As Richard noted, USB connected GPSes perform particularly poorly with ntp. Sadly, you can probably get better time from the internet than from a local USB GPS refclock. A 232-connected GPS without PPS would be better, particularly if configured with a sentence whose length doesn't vary like $GPGLL (use "mode 7" on 127.127.20.1 server line to enable all 3 sentences and configure the GPS to send only $GPGLL). I'm guessing you could get sub-millisecond accuracy with that route, after calibration. For PPS, the Garmin GPS 18x LVC is an affordable option, though it "only" claims one microsecond accuracy of the PPS signal, not tens of nanoseconds like timing receivers. With ntpd on windows you can't sync close enough for that to matter so far. With PPS, you should be able to stay within +/- 150 usec of UTC over 24 hours on Windows in my recent experience. Short-term jitter reported by ntpq -c peers is lower, 5-10 usec. Your mileage may vary, If the temperature is consistent day and night, for example, ntp will be able to keep offsets lower than if not. Systems with 10 msec clock period are currently worse off, but 15..6 msec is much more common. Cheers, Dave Hart _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
