A friend's post on FB made me recall a similar situation.

In his case, his IR-linked headphones now play a local AM station at very low volume whenever he's near an electrical outlet or switch in his house. Yes, it really happens, other people hear it too.

In my case, I recall a similar situation but I can't recall what the "receiver" was - it was in the 80s so if it was headphones it must have been wired but I don't recall having a walkman or similar at that time.

In any event, I can't seem to Google anything useful on this, although I'm sure I found an explanation in the 80s. IIRC, it was basically a crystal radio. It has to do with the contact between the wiring and the electrical boxes forming a cupric oxide diode, the wiring acting as an antenna, but I don't recall how you get the LC part. And then how would the headphones pick it up?

Does anyone have an actual explanation for this?

UPDATE: I woke up this morning and recalled the receiver in my case - the telephone. You could hear the local station very faintly in the background, but not over the sound of the dial tone.


the LC part comes about by capacitive coupling to ground that happens naturally when the wiring comes close to a piece of grounded metal, and the fact that even a straight piece of wire possesses a little bit of inductance. If the incoming AM radio signal is strong enough, even a badly-tuned LC tank circuit coupled to a poorly-fabricated cupric oxide contact diode will receive and demodulate enough of the signal to feed it into an incompetently laid-out and assembled ground system in a building, and hence bleed it into your audio feed.

The transistors in the first-stage preamplifier of a sound system can also act like diodes, and demodulate RF interference signals leaking into the circuit from poor grounding.

I know this from personal experience, having had to fix this problem in a church sanctuary in which the hearing aid transmitting loop encircling the room acted as an efficient radio frequency loop antenna, picked up the sunday morning (!) "Metallica Meltdown" show from a local AM station, and bled it into the ungrounded mic feeds leading into the sound system. we'd be sitting there in the Moment Of Silence and heavy metal headbanging music would be faintly playing out of the PA speakers...


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