[ntp:questions] How exact are the PPS pulses of common GPSses?

David Woolley david at ex.djwhome.demon.invalid
Thu Feb 14 07:39:24 UTC 2013

unruh wrote:

> 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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