"In college, I built small TV jammers. I'd go to the one dorm that had a color TV, sit in the back, in the dark, and tune in my jammer. The screen got messed up, not totally but enough to bother everyone. Without any plan, a friend in the front row, who knew what was going on (I hope he did) whacked the TV. I instantly turned the jammer off and the TV worked fine."
