J. Forster wrote:
From an unnamed, but VERY credible source:
"> It might be that the DoD is turning the civilian signals off in combat
areas to deny GPS to the Taliban and others.
Quite possible. This countermeasure was discussed more than ten years
ago.
It is possible to turn of the civilian signals -- or to leave then on
but _jam_ them within a selected area -- without interfering with US
military use of the satellites. A modern military does not need the C/
A code to acquire lock on a satellite. It can acquire the encrypted P
code directly."
The preferred method of controlling the access to GPS within a region is
GPS jammers, and the full set of efforts being spent on strengthening
the allied forces availability to signal is to ensure ability to survive
from jamming signal, which includes removing need for C/A locking prior
to Y-code lock with direct lock methods, transfer of time, solutions and
ephemeris data, and eventually means to direct additional power towards
the area and the improved M-code.
Turning of the C/A code of a satellite will effect the 1/3 of the earth
area that it sees, and for that to be effective in a certain area, you
need to do that to 6-8 sats to turn it off, and that will significantly
reduce the GPS availability for so large geographical areas that things
they want to work will run closer to failure. So no, turning of C/A code
is not what they want to do it. They can, but they want to avoid it.
Cheers,
Magnus
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