[ntp:questions] Sure gps looses all sattelite fixes

unruh unruh at invalid.ca
Tue Feb 28 06:06:55 UTC 2012

On 2012-02-28, John Hasler <jhasler at newsguy.com> wrote:
> unruh writes:
>> Surely it does not report based on predicted orbits.
> Predicted orbits from the ephemeris is all it has.  It has no way to
> actually track anything: it just has a single omnidirectional antenna.
>> I could imagine that the signal is too weak for timing but strong
>> enough to get location info from the sattelite.
> 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.

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

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. 

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