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Technology Stocks : Trimble Navigation
TRMB 68.25+1.0%11:59 AM EST
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To: David who wrote (1828)11/12/1997 6:55:00 PM
From: Robert A. Sutherland  Read Replies (2) of 3506
 
On the ground.. easy to deal with.

Munitions that use GPS may have some trouble, but usually have
backup and are fully hardened to EW. Some even have steerable
null arrays.

P-code does not mean militarized, it just allows you a mechanism
to deny your enemy access to "precise" GPS.

As far as militarization goes almost all of the "low-cost" receivers
are low-cost because they use digital correlation (1- or adaptive
2-bit) as opposed to the more expensive RF correlation architecture
(a separate RF-channel needed for each satellite, or some form of
multiplexing RF section) used in all "military" receivers. It's easy
to jam a commercial GPS receiver because they are essentially
limiting receivers and will capture the largest signal (FM/PM).

In a military receiver you "spread" the coherent jammer with the
CDMA code for the satellite you want to track, then filter out the
spread spectrum created (the satellites spread-spectrum has now
collapsed to contain the data rate, to around 20 Hz). If the jammer
is a C/A-code satellite code, you have to resort to the long sequence
P-code(so hopefully the receiver was initialized before being jammed).
For really nasty situations, since the jammer is a point source, you
just don't listen from that direction (a null-steering array).
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