Bob, Forgot to mention that this phase offset feature is built into the GPS receivers themselves.
Bye, Said Sent From iPhone On Sep 4, 2013, at 13:02, [email protected] wrote: > Hi Bob, > > it's not +/-100ns on all receivers. > > Our Fury GPSDO that uses Motorola designed M12M receivers allow +/-1ns > antenna delay phase adjustment resolution. No effect on timing stability. > > Almost all of our other products using uBlox GPS also allow +/-1ns antenna > delay phase adjustment resolution. > > It may take many minutes to track the new phase since typical GPSDO time > constants are set for 10's of minutes typically, but once settled, the > stability will not be affected by this phase offset. > > Bye, > Said > > > In a message dated 9/2/2013 15:24:01 Pacific Daylight Time, [email protected] > writes: > > 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. > > _______________________________________________ > 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.
