[time-nuts] Better GPS coming to phones

Attila Kinali attila at kinali.ch
Fri Sep 29 20:38:17 EDT 2017

On Thu, 28 Sep 2017 10:30:24 -0500
"Chris Caudle" <chris at chriscaudle.org> wrote:

> In a timing context, I would hope that having a more consistent solution
> to the position/time equation would reduce the PPS jitter.  It would be
> really nice to see one of these low power, high precision receiver devices
> used in a Thunderbolt style design that locks the chipset clock to the
> derived clock to avoid hanging bridges to see if the 10x better precision
> in location solution could result in 10x lower PPS jitter.

These chipsets are not designed to be used that way. They are ment
to have a fixed oscillator and will produce a PPS.

But hanging bridges is only an issue if you use the raw PPS pulse and do
not include sawtooth correction in your circuit. Any GPSDO worth its
salt will correct for sawtooth before using the timing of the PPS pulse
in its calculations.

There is one notable exception though: Brook Shera's GPSDO uses the spread
due to sawtooth to "enhance" resolution of the counter. Of course, that
makes it susceptible to hanging bridges. It still works very ok, especially
considering that, together with James Miller's GPSDO, it's the most simple
design out there.

				Attila Kinali
It is upon moral qualities that a society is ultimately founded. All 
the prosperity and technological sophistication in the world is of no 
use without that foundation.
                 -- Miss Matheson, The Diamond Age, Neil Stephenson

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