Mounted search and rescue

["IRVIN LICHTENSTEIN" <ilichten1@verizon.net>]

There were originally two features built into the GPS/Navstar system by the
military to preserve their advantage. Back when a unit was so big it had to
go on an aircraft carrier there were two message streams, precision, and
civilian.  The precision was for the military box and included some anti-jam
features. Since the first gulf war when the military started buying hand
held GPS at "Radio Shack" there has been no difference in the precision of
the streams and with the advent of competing European systems dithering the
clock to change accuracy is a thing of the past as well. You can buy
equipment that compares the two systems and decides which is right today. 

Also, the dependence on GPS locations for life safety automation in
aircraft, marine uses, and even by hikers and such companies as On-Star, and
various truck trailer trackers means playing with the signal does nobody any
good.  The more serious problems involve other RF devices, particularly
digital ones, that operate in the same band. The FAA puts boxes at the end
of runways that broadcast the difference between the GPS position of the
runway and the surveyed position just to aid landings.  

Irv Lichtenstein              ilichten1@verison.net