The GPS16 is not a timing grade GPS and only claims 1uS on the 1PPS. Given this, I think 0.5uS jitter and +/- 1.4uS wander is not bad.
cheers, ian http://www8.garmin.com/products/gps16/spec.html > > Message: 1 > Date: Thu, 01 Jul 2010 10:15:16 +0000 > From: Paul Nicholson <[email protected]> > Subject: [time-nuts] Long period variation of GPS PPS timing? > To: [email protected] > Message-ID: <[email protected]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > 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 > -- _________________________________________________________________ Browse profiles for FREE! Meet local singles online. http://clk.atdmt.com/NMN/go/150855801/direct/01/ _______________________________________________ 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.
