Originally Posted by
underfire
widespread or anything other than very, very local jamming would take an incredible amount of power.
Why do you believe that? Such a jamming signal would be competing with a power-budget constrained transmitter on satellites orbiting at approximately 20200 km altitude. I see commercial "GPS Jammer" pocket-sized handheld devices that apparently function effectively with 300mW output power on omni antennas. It would be a trivial RF engineering exercise to put out something quite a bit more, you could paint such a beam on any number of targets with a directional antenna.
The L1 carrier wave is at 1575.42 MHz. (wikipedia) In the frequency allocation filing the L1 C/A power is listed as 25.6 Watts. The Antenna gain is listed at 13 dBi. Thus, based on the frequency allocation filing, the power would be about 500 Watts (27 dBW). Now, the free space path loss from 21000 km is about 182 dB. Take the 500 Watts (27 dBW) and subtract the free space path loss (27 - 182) and you get -155 dBW. The end of life spec is -160 dBW, which leaves a 5 dB margin. (
GPS Satellite Power Output)
The low power level of GPS was discussed previously here, at:
http://www.pprune.org/tech-log/48302...hosen-gps.html