[time-nuts] GPSDO+PC as a NTP server

[David J Taylor]

From: Fiorenzo Cattaneo
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GPS and GLONASS are the best GNSS around, they are operated by the
military as a military operation and have the best reliability record.
Beidu is fairly new, and Galileo is operated by civlian agencies.
They've had major operational issues. So this leaves GPS and GLONASS.
GLONASS tends to have better coverage on the polar regions, but
otherwise I think GPS is better, and GPS has better time and space
accuracy. Although I'm not that with the accuracy of RS232 interrupt
handling it would be possible to even tell the time differenbce.
between UTS(GPS) and UTC(GLONASS).

I'm not even sure than running GLONASS and GPS together will give you
a better time solution, although it will definitely improve
availability.
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GPS, GLONASS and Galileo have /all/ had operational difficulties, and 
possibly BeiDou too.  For precision timekeeping Galileo has the best 
on-board sources, but using GPS and Galileo is perhaps the best combination 
of accuracy and reliability.  The offset between GPS time and UTC, and 
Galileo time and UTC is regularly reported (possibly in the satellite feed 
itself).  It's nanoseconds, and very unlikely to affect a system using a PPS 
signal from a typical amateur cost source.

I think you underrate Galileo, certainly in suggesting GLONASS above 
Galileo.

  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6308660/
  https://www.itnews.com.au/news/satellite-failure-caused-global-gps-timing-anomaly-414237
  https://www.theverge.com/2019/7/15/20694395/europe-galileo-satellite-navigation-system-offline-outage-technical-incident


Cheers,
David
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