I live about 500 feet away from my university's radio station (KZSC 88.1) and everybody in my building gets the radio very faintly in our speakers. I told my dad (an electronics nut) about this and he sent me some cable shielding which got rid of the problem. However, I still have a few questions that he didn't know:

1) Why is the radio audible? The signal is FM, so what de-modulates it?

2) My dad said to make sure to ground the shielding. But wouldn't un-grounded shielding work also? (I'm thinking of a Faraday-cage effect) I can see that it might not be as good, but would it work at all?

I don't know much about electronics, but I did take a physics class which went over electricity.

Thanks!

I have the same problem, how do I shield the cables? I hate the FM noise...

As for the demodulation: I never heard AM interference noise... I suppose FM signal is better suited to drive a speaker.

The easiest way to shield the cables is to buy shielded cables... however, my dad had some cable braid sitting around (no clue where he got it) so he sent it to me. Then I stuffed the cable through the shielding, which was not easy. The braid acts like those Chinese finger traps, and kept tightening around the connector as it went through.

I really don't know where to get cable braid, but Radio Shack tends to have stuff like that; you might find some there.

Just remember, if you do find some shielding, make sure to ground it. It won't work particulary well if you just have it sitting on the wire.

Demodulating FM is not particularly complicated. All you need is to take the FM signal and pass it through a circuit with linear (or nearly) voltage to frequency response followed by soem sort of envelope detection. Many parts of a speaker crossover could have the required characteristics.

Intermod is very common close to the transmitter. Around some antenna farms notably wilson in LA and ______ in Albany there is a strong inter mod effect. I have noted in my own experience that even with no anntenna attached to a hard tuner that the chassis itself behaves as an antenna and certain stations are audible, some even clear. Of course once the chassis is being used as an antenna the problem of hand-capacitance becomes more signifigant.


as a further note, I know that many college stations use a so-called "leaky fm" cable cast to their dorms which is emitted through the power supply to each room. Their signal may also be available in this fashion. This can unfortunatly make it present in an improper gound connection to the Amp or other connection.

To add a funny and strange note I've seen on TV somewhen:
There was a woman who heard voices from her pot in the kitchen and she almost thought there were ghosts. The pot was receiving the signal from a nearby radio station.
It was a reliable programme about spooky things.