One of my speakers has been picking up a radio signal. It is connected
with my computer and works fine with playing sound. There is no
program running that would be causing this effect and even when I
completely mute the sound system on my computer an unidentified radio
station will play on it.

How is this physically possible?

Hi toolofthesystem-ga,

This phenomenon is known as "radio frequency breakthrough
interference". It occurs because the speaker leads are acting as an
antenna and picking up the radio wave, converting it to an electrical
signal.

There is then some kind of nonlinearity which demodulates the radio
wave, producing the audio component. This could be, for example, a
corroded joint acting like the crystal in a traditional crystal set
and rectifying the radio frequency signal, producing an audio
frequency signal that makes a sound when it passes through the
speaker.

The following short article may prove useful to you:

   Solving Radio Interference RFI Breakthrough on Computer Speakers
   http://www.stevelarkins.freeuk.com/computer_interference.htm

I trust this provides the information you are seeking. If not, please
request clarification.

Regards,
eiffel-ga


Google Search Strategy:

radio interference breakthrough speakers
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I presume your speakers have a built-in amplifier. The nonlinear
distortion that demodulates the AM radio station is probably in the
front-end transistor of that amplifier.