Chris, I think you are onto something. Running Lady Heather on this unit I see a line under “receiver” with the term “SawT” and a parameter of 24ns. So if we combine this information with what you teach below, it’s starting to look like maybe the M12 unit is doing something different than the Lucent. I am watching it today and I see 5 PPS that vary from the lucent pulse (used as a trigger) each about +20ns until it resets.
Mark Sims, can you comment on the SawT parameter, I assumed being reported by the M12 GPS, displayed on Lady Heather? Thanks > On Jun 5, 2017, at 10:15 AM, Chris Albertson <[email protected]> > wrote: > > I did not finish the sawtooth explanation. One of the units is designed > such that the PPS is always on the raising edge of an internal 10MHz clock. > If the 10MHz clock were perfect this means the maximum error is 1/2 > cycle. The software in the GPS choose site best edge to minimize error. > the jump you see it when it selects a different cycle and jumps The > software tracks the error and outputs an estimate of the root on the serial > channel. > > You can verify this by plotting the sawtooth correction vs.time and see > that it lines up with your observation of the jump back to zero error. > > There might still be errors cause by other things, like improper self > survey but the results you reported are exactly like what one would expect > from a unit that uses an oscillator edge to trigger PPS. It other words > what you see is a design feature not an error. > > On Mon, Jun 5, 2017 at 6:40 AM, Jerry Hancock <[email protected]> wrote: > >> It was off 7.5KM, that’s a little beyond groggy, no? More like a trip to >> Vegas. >> >> I’ll let it rerun the survey and see if it gets closer. >> >>> On Jun 4, 2017, at 9:50 PM, Mark Sims <[email protected]> wrote: >>> >>> Be careful when using one unit's location to set a different model's >> location... particularly the altitude. Some devices report altitude in >> MSL, others in AGL... and different units may use different models for the >> ellipsoid. You are always better off using coordinates generated by the >> particular device (either the built-in self survey or something like Lady >> Heather's precision survey). >>> >>> I did some tests while developing Lady Heather's precision survey code. >> I got pretty consistent lat/lon/alt results on the same units but >> consistent offsets between different models of receivers. >>> >>> I would suggest letting the Motorola re-surevy itself... it may have >> been a bit groggy after first being powered up after a few years of >> sleep... I know I am... >>> >>> --------------- >>> >>>> I then set the M12 reference location to the Lucent location as I know >> it to be correct. >>> _______________________________________________ >>> 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. >> > > > > -- > > Chris Albertson > Redondo Beach, California > _______________________________________________ > 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.
