[time-nuts] Adafruit Ultimate GPS timing message arrival times

Chris Albertson albertson.chris at gmail.com
Mon Aug 1 12:43:35 EDT 2016

As an exercise it might be fun to try to do the best you can with just
NMEA.  But practically speaking even my very  $10, 8-channel motorola
GPS receiver can output a PPS to about 50ns.  Better then needed for
NTP.   You friend in the Gobi desert would be better off my $10 GPS

That said, if you had a good local oscillator you could make a decent
GPSDO using NMEA only with a VERY long time constant

On Mon, Aug 1, 2016 at 9:23 AM, Mark Sims <holrum at hotmail.com> wrote:
> Well,  the whole point of the exercise is to see how well you can do if you DON'T have an internet connection, a 1PPS signal,  or a stratum 1 time server available...  only the humble messages coming from a 10 dollar GPS receiver.  Try getting a net connection in the middle of the Gobi desert (where one user uses Lady Heather's time sync feature to keep their system clocks reasonably accurate).
> If you can put the receiver into a binary message mode, you can usually do better than NMEA (but, surprisingly, usually not by much).  And by selecting a receiver that has known good / stable message timing you can do surprisingly well.
> ----------------------
>> I feel that using the serial NMEA stream would, today, be a last resort, as an Internet sync would be considerably better.  Would you agree with that?
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Chris Albertson
Redondo Beach, California

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