soxinbox wrote:
In non aviation GPSs, at least the older ones, there really is a limitation
on speed. These units receive the signals from satellites one at a time. You
have to receive 4 satellites in order to calculate a 3 dimensional position.
If you are traveling extremely fast, than the signals from each satellite
are received at different physical positions. This makes it hard for the GPS
to resolve your position. Now here is the clincher : The speed at which the
GPS unit can switch between satellites determines the top speed at which the
GPS unit will work.

Aviation GPS units have simultaneous receive channels so that they can
receive up to 7 ( usually ) simultaneous signals.


They do now. The first couple generations of aviation GPS's had those
receivers. The one I had was the Garmin 90. When I went to the Garmin
Pilot III it could simultaneously receive 12 sats. They all do that
now. What's funny is to look into the consumer GPS market, especially
bluetooth GPS's designed for use with a PDA or similar. The most
expensive models can track 30 satellites at a time.