AKA spark gap generators. Take $50 worth of parts, connect it to a lightweight motorcycle battery, throw it in a backpack, and you've jammed all useful frequenc

AKA spark gap generators. Take $50 worth of parts, connect it to a lightweight motorcycle battery, throw it in a backpack, and you've jammed all useful frequencies within several hundred yards of your transmitter. You can even jam military satellite communications with a surprisingly reasonable budget (sub-$10,000). The only defense is the fact that the signal source's location is incredibly conspicuous, thus easy for the military to blow up but civilians can't exactly rely on EM-homing missiles to keep their lines of communication open.