> The deal is that the military just doesn’t use filters
Do you have a citation for that?
I would have thought the issue is not that GPS receivers don't use filters, but rather than no filter has a perfectly sharp cut-off and GPS signals are exceptionally faint.
For example, if the GPS signal is 0.1 femtowatts at 1575MHz, even if you've got a filter that can remove 99.99999% of a noise signal at 1600MHz you can still overwhelm the GPS signal with 1 nanowatt of power.
Precisely -- no RF filter has a perfect "brick wall" response, and no transmitter will have a perfectly pure output either. GPS receivers already have to use some pretty crazy tricks to pull a signal out of the noise; it doesn't take a lot of interference to make that impossible.
Oh man, I bet there's a nice market of GPS jammers out there - especially useful for the home team in any action, since they don't need help with directions. I wonder if that counts as a weapon?
Some truckers use them for manipulating the trackers on their vehicles. Some of them are stupid enough to have them active when they are anywhere near an airport, which makes it far more likely they'll get caught.
Do you have a citation for that?
I would have thought the issue is not that GPS receivers don't use filters, but rather than no filter has a perfectly sharp cut-off and GPS signals are exceptionally faint.
For example, if the GPS signal is 0.1 femtowatts at 1575MHz, even if you've got a filter that can remove 99.99999% of a noise signal at 1600MHz you can still overwhelm the GPS signal with 1 nanowatt of power.