Land Rover in C-130 commercial

At one time . . . and perhaps still . . . many GPSs for the civilian
market had a firmware limit on velocity . . . supposedly to prevent the
use of such a unit in a weapons system. I recall a number of around
900 knots . . . but do not hold me to that. My old Garmin 45 and 48
had it. Not sure about my newer ones.

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

This is an artificial limit that manufacturers design into their GPS units
to force you to pay a premium for a device that can be used in an aircraft.

Mike Schumann

"Jim Macklin" wrote in message
news:Wksbg.22187$ZW3.9577@dukeread04...
I have no doubt that they did drive a car into a C130. I
just question whether they went to the trouble to have the
GPS in the car actually work while in the cargo bay.

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.



--
James H. Macklin
ATP,CFI,A&P

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"Kingfish" wrote in message
ups.com...
| It is simulated, phony, ...
|
| I dunno, the documentary of the filming of the commercial
seemed legit.
|
|
| My recent hand held non-aviation GPS has a limit of 951
mph.
|
| What is the limit due to? Is there a refresh rate for a
GPS receiver?
| Is it a RAIM thing?
|

"Mike Schumann" wrote in message
nk.net...
This is an artificial limit that manufacturers design into their GPS units
to force you to pay a premium for a device that can be used in an
aircraft.

That may have been true in the past. I recall marine units that had a very
low limit.

However, I have a handheld hiking unit that has a plenty high limit (don't
know what it is, but it works fine in the plane and even will show me my
speed in knots), and that explanation certainly doesn't seem relevant to the
951 mph limit mentioned previously in this thread (unless the market they
want to exclude are military and Concorde pilots).

Kingfish wrote:
After seeing this commercial and viewing the documentary on the Land
Rover website, I still can't figure out how they got the GPS unit in
the truck to work while inside the plane. The doc. showed a guy
sticking something to the plane's windows that might be an antenna, but
I doubt a dash-mounted GPS in a car would have an external antenna
input? Also they said the speed of the plane might be an issue for the
GPS. Can't figure that part out either.


Several thoughts:

1 - The display was probably simulated.

2 - HOWEVER! One doesn't need an antenna jack with a re-radiating antenna:

http://safetracgps.com/Vortech.htm

I have one, and it works great. If the display wasn't simulated, the
Vortech could have been re-radiated the GPS signal inside the airplane,
making the car's GPS work correctly.


3 - But then again, EVERY dash mounted OEM auto navigation system
actually does have an antenna jack, it's wired to the _vehicle's_
external GPS antenna. G

Kingfish wrote:
After seeing this commercial and viewing the documentary on the Land
Rover website, I still can't figure out how they got the GPS unit in
the truck to work while inside the plane. The doc. showed a guy
sticking something to the plane's windows that might be an antenna, but
I doubt a dash-mounted GPS in a car would have an external antenna
input? Also they said the speed of the plane might be an issue for the
GPS. Can't figure that part out either.

I have a very old GPS that has a speed limit of 105 I think....
something in the low 100's ... I know me and a friend exceeded it in his
BMW 3 series. However, pretty much any modern GPS has a speed limit in
the 900 to 1000 mph range. I would think that an in dash GPS very well
may have a remote antenna. Inside the dash could be a much worse
location than on top of the dash. I would bet the antenna is directly
under the plastic dash cover up as high as it can be in the center of
the window or it could be up on the top somewhere. Either way wouldn't
surprise me. Except for the Etrex and tiny units like that, I think all
the bigger Garmin units all have an external antenna jack.

I still think the TV ad is stupid. You can do the same thing with a sub
$100 hand held GPS or a 300 year old sextant (they did have sextants
back in 1706 didn't they?), a $5 watch and some charts.


--
Chris W
KE5GIX

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