[time-nuts] PPS sync

[Chris Albertson]

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 <jerry at hanler.com> 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 <holrum at hotmail.com> 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.
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-- 

Chris Albertson
Redondo Beach, California