[aprssig] Differential GPS?

Wes Johnston, AI4PX wes at ai4px.com
Fri Apr 24 07:41:50 EDT 2009

Anyone been outside the USA lately?  Is SA still on in the rest of the

Just for a trip down memory lane... I remember back in 1997 time frame when
they were searching for the a-10 warthog that crashed in the rockies that my
truck's parked position went from wandering in a 300' circle to less than
60' in a matter of an hour and stayed that way for several hours.  The
reason given for this was to allow the SAR team's GPS units to get a better
fix.  Lead me to believe that they had to switch off SA on the birds as they
came over the control station.  This in turn leaves me wondering if the
satellites are scheduled to turn off SA at specific times of day (ie when
they are projected to be over a specific theater of operation).  I seem to
recall that upon the announcement that SA would be switched off, it was
quietly mentioned that it could be turned on over specific areas.

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