Back in the late 50's the Heathkit company had a "build-it-yourself" radio kit based on the early TRF (tuned radio frequency) radio. For you younger guys, these radios were not superhetrodyne like our modern radios where one only has to rotate a single knob to change stations. With the TRF one had to tune each stage of amplification to the frequency of the desired radio station. At any rate, I bought one of these kits when I was in the Air Force and found, quite by accident, that if I tuned to a radio station that one of my buddies was listening to in the barracks, and then detuned slightly, I could jam his radio. Drove him nuts! But the best part came later when, on one weekend I looked out of the barracks window and, lo and behold! there was a guy washing his car while listening to his radio. Ha! So, I got out my trusty TRF, found the frequency the car radio was tuned to - AND JAMMED IT! Today, that guy is still wondering what the hell was wrong with that radio. I never tested at what range I could jam radio channels, but the car was a good 100 feet away. Now, this device will work with AM radios but not with FM, unfortunately (not without a lot of modification of the TRF).