All the press monkeys were in such an uproar over "GPS jamming systems". While I'm sure all the journalism majors were surprised, I wasn't when we announced their atomization.
Ok, cluebat time folks... "jamming" a radio signal works* by flooding a certain frequency with a signal stronger than the one you want to listen to. When you are driving down a highway and one radio station gradually replaces another in your car, in a sense the new radio station is "jamming" the old one.
Let's say you were really really ticked off at, say, WJFK because you hate Don and Mike, and you wanted to just completely shut them down. All you'd need to do is get a transmitter to broadcast static on the same frequency as WJFK, and have that signal be more powerful than the radio station's. When you turn your transmitter on, suddenly everyone within a certain distance to your transmitter listening to WJFK is now listening to static. You're jamming the signal.
Now, note for this to work you need a transmitter. Something that emits a signal stronger than the original. As anyone who has ever tried to pick up a ballgame on one of those portable TVs knows, most types of radio signals are directional. A jammer by definition has to be pretty powerful to work at all, so it's usually pretty trivial to triangulate the location and shut it down. If you're the FCC, you use guys in suits.
If you're the military, you use a bomb.