Just got home from work, so this is going to be a quick and dirty post. Its 1:30 in the morning here in California.
Watch this video.
The guy is nice enough to show you how to build the device and shows you how it works in this video.
He even specifies an antenna length (52 inches or 132 cm), but he cleverly doesn't show you the chip manufacturer or chip number, and also leaves out the value of the vari-cap.
I'm going to alleviate that issue.
The chip is a 7404 Hex Inverter and the vari-cap is rated at 1-30pF.
This will also jam older over the air analog TV signals (there are still some low power stations here in the US). It will not work on over the air digital TV broadcasts.
It will only jam stereos that are playing radio signals, not tapes, MP3s, CDs, etc.
A guy I work with said there is a way to defeat even those, and its played on my mind. I'll have to have him elaborate, because the only way I can think of doing it is using an EMP and frying everything.
Anyways, good night!