Why in the hell is my box fan picking up radio waves?

[BrantheMan]

I moved into my new apartment about a month ago. Not long after moving in, I would be lying in bed with my fan on and would hear faint sounds of music and voices. I thought it was just in my head since I was sleepy.

But it started getting louder and louder over time. One night, I got up -WIDE AWAKE- and listened to some radio station via my box fan. I began walking towards it, and the music suddenly stopped when I was inches away from the fan.

When I stepped back, it would continue again. Now I was convinced.

I got my sister, who was still awake downstairs, to come to my room and verify what I was experiencing was real.

Sure enough, she heard it too. When we unplug the fan, the music/talk radio stops. When we plug it back in, it resumes.

I've searched all over the internet for an answer. Me and sister have since shown this phenomena to a few more friends, who ALSO confirmed it.

All i've gotten when searching online is other people asking the exact same question but with no answer...so apparently this isn't that "rare" of a thing.

Does anyone know how in hell local radio stations are transmitting through my FAN?

 

[KenE]

Your box fan is plugged into the mains. There is almost certainly a radio transmitter fairly close to your new home, it is almost certainly AM, not FM, but it may be a short wave transmitter using AM. The mains cable and probably the mains themselves are acting as an antenna. This is not rare, some household radios used the mains as an antenna, though that often gave a noisy signal.

AM stands for "amplitude modulation". See the Wikipedia article for more details, but AM is easily turned back into an audio signal by any device that is a one-way conductor of electricity. Such one-way conductors might be used in speed controls of fans, or they can be just a poor contact in some part of the fan wiring.

Now I am not sure what you mean by a "box fan". I'm guessing that it is what we call a fan heater in this country, though it might not be. It probably does not matter anyway.

At some point inside the wiring of your fan, maybe in the speed control there is a partially conductive circuit that is rectifying the signal from the radio station and some of this rectified signal, which is now direct current, is making the coil in the motor, or maybe the heater elements vibrate. This vibration is in the audio range and you hear it as sound.

This sort of thing is not all that rare, but it is difficult to diagnose unless you have exact knowledge of where the radio station is and exactly what circuits are used in the fan.

AM and in fact all radio transmitters emit radio waves in magnetic and electrical form. The effective range of the magnetic part of the signal is not great, generally only a few hundred metres, but the effective range of the electrical part is hundreds or thousands of kilometres. Perhaps the mains goes past the transmitter. But if the transmitter is more than a few kilometres away some kind of amplification is usually needed, and your fan probably does not have that. So I am guessing your fan is fairly close to a transmitter.

The length of the fan cable plus some part of the mains may be "tuning" the fan into a particular station. This is because radio waves from a transmitter have a particular wavelength and most professional antennas at shorter wavelengths are cut to suit the wavelength. When you get close to the fan, the combined capacitance and inductance of your body detunes the system and the signal disappears. If you wind most of the fan cable into a coil and try that the sound will more than likely disappear too as that changes the electrical "length" of the cable.

If there is more than one transmitter nearby, it's possible that if you listen very carefully you will hear two stations at once, since your fan is not "tuned" to any particular transmitter.

Most of a conventional AM radio is taken up by tuning to separate stations from each other and amplification to bring in weaker signals. The detection part which turns the signal from radio frequency to sound frequency is the easy bit.

 

[KenE]

Your box fan is plugged into the mains. There is almost certainly a radio transmitter fairly close to your new home, it is almost certainly AM, not FM, but it may be a short wave transmitter using AM. The mains cable and probably the mains themselves are acting as an antenna. This is not rare, some household radios used the mains as an antenna, though that often gave a noisy signal.

AM stands for "amplitude modulation". See the Wikipedia article for more details, but AM is easily turned back into an audio signal by any device that is a one-way conductor of electricity. Such one-way conductors might be used in speed controls of fans, or they can be just a poor contact in some part of the fan wiring.

Now I am not sure what you mean by a "box fan". I'm guessing that it is what we call a fan heater in this country, though it might not be. It probably does not matter anyway.

At some point inside the wiring of your fan, maybe in the speed control there is a partially conductive circuit that is rectifying the signal from the radio station and some of this rectified signal, which is now direct current, is making the coil in the motor, or maybe the heater elements vibrate. This vibration is in the audio range and you hear it as sound.

This sort of thing is not all that rare, but it is difficult to diagnose unless you have exact knowledge of where the radio station is and exactly what circuits are used in the fan.

AM and in fact all radio transmitters emit radio waves in magnetic and electrical form. The effective range of the magnetic part of the signal is not great, generally only a few hundred metres, but the effective range of the electrical part is hundreds or thousands of kilometres. Perhaps the mains goes past the transmitter. But if the transmitter is more than a few kilometres away some kind of amplification is usually needed, and your fan probably does not have that. So I am guessing your fan is fairly close to a transmitter.

The length of the fan cable plus some part of the mains may be "tuning" the fan into a particular station. This is because radio waves from a transmitter have a particular wavelength and most professional antennas at shorter wavelengths are cut to suit the wavelength. When you get close to the fan, the combined capacitance and inductance of your body detunes the system and the signal disappears. If you wind most of the fan cable into a coil and try that the sound will more than likely disappear too as that changes the electrical "length" of the cable.

If there is more than one transmitter nearby, it's possible that if you listen very carefully you will hear two stations at once, since your fan is not "tuned" to any particular transmitter.

Most of a conventional AM radio is taken up by tuning to separate stations from each other and amplification to bring in weaker signals. The detection part which turns the signal from radio frequency to sound frequency is the easy bit.