[ntp:questions] Sure gps looses all sattelite fixes

John Hasler jhasler at newsguy.com
Tue Feb 28 13:26:28 UTC 2012

I wrote:
> It doesn't get location data from the satellite.  It uses the
> ephemeris[1] to plot satellites that should be above the horizon.
> [1]Updated periodically, of course.

unruh writes:
> Updated how?  The only thing it could update them from is the sattelites
> themselves. So the sattelites DO give their location to the system.

Every satellite preiodically transmits the full ephemeris for all the
satellites, not just its own, and the receiver retains it until it gets
a new one or it expires.  Thus it can have been quite a while since your
receiver has gotten data from any satellite but it will still know where
they all are.

> And why does the Sure plot 12-14 sattelites at all times while the
> Gamin only does 9-11? both have the same sattelites above the horizon
> at any one time. And the sure plots them right down to the horizon (
> and gets signals from them) while the Garmin only reports them down to
> about10 degrees above the horizon.

Most likely because Sure decided to show you all above-horizon
satellites while Garmin decided to show you only ones they think are
high enough to be useful.
John Hasler 
jhasler at newsguy.com
Dancing Horse Hill
Elmwood, WI USA

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