[ntp:questions] How exact are the PPS pulses of common GPSses?
david at ex.djwhome.demon.invalid
Thu Feb 14 07:39:24 UTC 2013
> If it were out by 1us, it would put you out by almost a km on the
> surface of the earth.
That's a requirement for the relative time from two satellites. The
absolute time and any propagation effect that is common to all
satellites in view, can have a higher error than that that implied by
light travel time effects. Time errors in common across all in view
only produce errors proportionate to the orbital velocity, not to the
speed of light.
I once found an official Navstar document that suggests that, for time
transfer purposes, GPS is good to 50ns. These were figures for SA off,
although the document was from the SA area. I think they were for a
relatively short averaging time.
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