One of the GPS units is likely sending a saw-tooth message out the serial line that exactly describes the 0 to 100ns drift. This is why they call it "saw tooth" the function ramps up slowly then falls to zero. A device like a GPSDO that uses the PPS would need access to the serial data to read the sawtooth correction,
On Sun, Jun 4, 2017 at 9:36 PM, Jerry Hancock <je...@hanler.com> wrote: > 1) I have my TAPR M12 Kit working now next to my lucent RFTG-U REF0/1 > pair. I was comparing the PPS outputs triggering on the Lucent as channel > 1 and the M12 as channel 2. I can’t tell which is moving around but the > symptoms are that at T0 (not the top of the minute or hour) they are in > sync within a nanosecond. From T1 to T20 they move progressively out of > sync until hitting around 100ns and then snapping back to being in sync. I > would think that if both were moving that it wouldn’t be that consistent, > no? > > Since I can’t tell which is moving, most likely both, I plan to take the > disciplined 10Mhz out of the Lucent and divide it down with my TAPR TADD-2 > to 1PPS. I would think that would be more stable on a PPS by PPS basis and > compare again. > > Any other ideas? > > 2) When I first fired up the M12 and let it do a survey, it was off for > some reason by 7KM. I then set the M12 reference location to the Lucent > location as I know it to be correct. I was thinking though, would the PPS > phase comparison in 1, above, be impacted by the reference locations being > off? Both GPS cables are the same length. The only thing I don’t know is > the internal processing delay of the units. The SynTac software allows you > to take this into consideration for PPS timing when using the M12. > Interesting unit by the way. Lots of configuration options exposed with > the Syntac software. Not that I would replace Lady Heather or anything, > I’m just using it while I get some of these issues figured out. > > Jerry > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.