Bob, The 5ns time stamper data attached shows a 500 second hang in the 1PPS phase from an M12+. A graphic example of why including sawtooth correction in a GPSDO is a good idea. With 500 samples having an offset even long filter times create a source control error unless the offset is corrected in the samples before entering the control loop.
Richard > The smart guys have already contributed to this thread. What I have is an > example > taken when I was doing some testing. The plot at the top is the DAC on my > GDPSO. > It is moving the oscillator back and forth about 4.6E-4 Hz. Not a lot. > > The bottom plot is the interesting one, as it is the 1PPS from my Adafruit Nav > Receiver plotted with respect to the OCXO. The labeling is unfortunate for > this > discussion. Just think of "-10" as being +180 degrees of phase, and -30 as > being > -180 degrees, for a total phase of 360 degrees between them.. Notice the > plot at > about 10:40. It points out that the 1PPS error isn't nicely spread out. > Rather, > it moves around as the difference between the time signal being received from > the > satellite and the free-running oscillator in the GPS receiver > > http://www.evoria.net/AE6RV/GPSstd_PLL/Plots/PPS%20Anomaly%202.png > > > Bob > > > > >>________________________________ >> From: Jimmy D. Burrell <[email protected]> >>To: Discussion of precise time and frequency measurement <[email protected]> >>Sent: Sunday, February 16, 2014 1:55 PM >>Subject: [time-nuts] GPS accuracy specs >> >> >>I've looked at several different manufacturer GPS datasheets now regarding >>the 1 >> PPS output in an attempt to compare apples to apples. Some of them rate >> their 1 >> PPS output as something on the order of "PPS signals have an accuracy ranging >> 10ns" which seems ambiguous. Does that mean the leading edge of their 1PPS is >> within 10ns of the GPS clock? Or simply that the stability of their 1 PPS is >> within 10ns? Or both? >> >>Perhaps there's an industry standard for these specs of which I'm unaware? >> >>The datasheet for my (presumably much older) Globalsat ER-102 seems, to me at >> least, to be much more clear stating "time reference at the pulse leading >> edge >> aligned to GPS sec., +/- 1 us". Which I interpret as the leading edge of my >> receiver's 1PPS is aligned with the GPS's clock to within +/- 1 us. >> >>Jim... >>N5SPE >>_______________________________________________ >>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. >> >> >> > _______________________________________________ > 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. >
<<attachment: Sawtooth.gif>>
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