"Steven Shelikoff" wrote in message
...
On 20 Dec 2004 07:58:48 -0800, wrote:
It does get locally turned off once in a while for tests, military
exercises, etc. Usually they give plenty of warning. For instance,
here's an AP line about an outage back in June for the Carolinas to
Florida:
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Military testing system designed to jam GPS signals off coast
WILMINGTON, N.C. (AP) - Military officials are testing a system for
jamming signals from navigational satellites - an experiment that could
disable boaters' GPS devices and force them to rely on dead reckoning.
The test began Friday and will run through June 20, as part of a NATO
training exercise along the Atlantic Coast.
The Coast Guard said GPS signals will be unreliable or unavailable in
waters up to 60 miles off North Carolina and along the coast of northern
and central Florida. Officials said the testing may affect cell phones
as well as GPS navigation devices in boats, airplanes or cars.
Coast Guard stations are trying to get word out about the interference.
"What we kind of foresee happening is some confusion on the mariners'
end," said Petty Officer 1st Class David Christensen.
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And mo Would anyone want to be in a commercial or private airplane
when making an initial approach in low ceiling weather to landing and
having GPS suddenly go off? This may well be an "end."
No, that won't be the end either... unless the plane doesn't have a
pilot and it's being flown automatically, directed by GPS.
Steve
Actually Steve I think the military jammed the signal rather than turning it
off or degrading it. I also believe that there are antennas that would make
it difficult or impossible to jam a GPS particularly from a boat a few miles
away from the jamming site. I doubt the military will talk about it but
reasonably simple shielded antenna with deliberate limitation of the sky
viewed can probably provide pretty good reception even in the face of heavy
jamming.
On the other side jamming GPS in a relatively close in situation like a
harbor or a city is a piece of cake. I am sure the hacker community already
has a couple of desings on the internet.
None of this in any way applies that the gov can't easily screw around with
the signal to any desired extent. I would also point out it would be
relatively trivial for the gov to take out Russian or European sattellites
as well. Probably construable as an act of war but why else would the gov.
do it?
Jim Donohue