Hi On all the GPS's I have tried it on, shifting the PPS has no real impact on stability. A few things to consider:
Normally the shift is a few hundred ns either way The shift process is always in steps of the main clock (100 ns for 10 MHz) GPS by it's self bounces around a bit. If you are talking about a shift of a big fraction of a second (and it sounds like you are) then the stability of the GPS's local clock could come into play. On something like a TBolt that's not going to matter. On a TCXO based gizmo that is only corrected to 1.0x10^-7 you could get an extra 50 ns of error at a half second offset. Weather you see that on this or that GPS depends a lot on who wrote the firmware and what they worried about when they did. The better alternative is to use a counter with a reasonable time base to look at the difference between pps signals. If the counter has an OCXO time base and it's properly calibrated you are about 10 to 100X better off than the 50 ns in the example above. Bob On Sep 2, 2013, at 6:05 PM, Lachlan Gunn <[email protected]> wrote: > Hello. > > > > Has anyone here tried varying the PPS offset on a ResT (or UT+ or any other > GPS receiver for that matter) and measuring the resulting stability? > > > > I ask because my Rb has only a 1PPS output, and while I have been able to > get at one of its internal HF signals, would like to see what I can do with > just 1PPS. The obvious problem with doing this is that I will need to align > the PPS outputs together to get reasonable accuracy, but I worry that a > large offset in the GPS receiver will degrade stability as the pulse moves > away from the relevant packet in the GPS signal. > > > > Am I being over-cautious? > > > > Thanks, > > Lachlan > > _______________________________________________ > 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.
