Land Rover in C-130 commercial

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. This eliminates the speed
restriction ( unless you are traveling close to the speed of light). I think
the simultaneous receive channels is starting to be used in higher end
non-aviation GPSs, perhaps like the one in the Land Rover.

In response to another posters comments about the reception inside the
plane: Most auto GPSs do have external antennae ports. It is just as hard to
get a signal through the top of a Land rover as it is a C130. My handheld
hiking GPS also has an antenna port.

"Peter Duniho" wrote in message
...
"Jim Macklin" wrote in message
news:Wksbg.22187$ZW3.9577@dukeread04...
As for the speed limit on the GPS, I presume it is the rate
at which the computer can identify new positions and the CPU
can calculate, it is just a cheap $125 hand held.

That doesn't make any sense. You can measure your position every 30
seconds and still get an accurate speed measurement.

Whatever the reason for an upper bound on the displayed speed, it has
nothing to do with the rate at which the computer in the GPS can do
anything, whether identifying new positions, calculating, etc.

Pete

"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.

My son has a Palm Pilot V that has the GPS receiver plugged into the
expansion port. On a737, I was able to hold it up to a window, and get
altitude and speed locks, no problem, showing 540 MPH.
--
Jim in NC

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.

"soxinbox" wrote in message
...
In non aviation GPSs, at least the older ones, there really is a
limitation on speed. [...]

You are right about the older satellites. However, that explanation is
irrelevant for the GPS being discussed here. Also, I don't see why the
limitation you're talking about would manifest itself as an upper bound on
the speed display; it would simply result in no position information at all
above a certain speed.

Pete

"Peter Duniho" wrote in message
...
"soxinbox" wrote in message
...
In non aviation GPSs, at least the older ones, there really is a
limitation on speed. [...]

You are right about the older satellites.

"Satellites", "receivers", same diff.