How did I turn myself into a radio? Why can I listen to the radio through my body?

Question

Probably like most of you, I have a lot of old headphones that are broken in some way or another. I have been looking for something creative to do with them for a while and today I made the dive.

So yea. I just ripped the end off of some headphones, soldered a connection to a copper penny, then super-glued the penny onto some old headphones.

Next, I plugged my headphone jack into my computer, and for fun, pressed both pennies against my arm. Sadly, they didn't pick up anything but noise (or if they picked up more than noise, I didn't notice).

Next I decided to add two passive low-pass filters to the circuit. I have no idea why these would make any difference but here they are. There are two resistors in series (2x220 ohms) followed by a 10 uF capacitor for each input channel. Here's what I heard this time: Sound

To my surprise, it appeared I was picking up some kind of radio station? What's happening here?? Can anyone explain why this is?

Edit2: I also want to add that this only happened in an upstairs room of my home. It didn't work when I carried my laptop downstairs. It's possible this could've been related to the way I was sitting (and how the electrodes' wires ran away from my body), the fact that my laptop was plugged in when I was upstairs and not when I moved (60Hz noise added power to the signal through some sort of wavelet addition?), or when I went downstairs the signal was less intense because of some unpredictable location attribute (e.g. an upstairs neighbor playing the radio next door). My favorite theory though is that this is somehow due to the EMF running along the outside of our skin. Can anyone disagree?

Answer 1

Your experience is entirely plausible, I have experienced it myself, though with somewhat different equipment. Like you, the first time I experienced it, I was completely flabbergasted.

As it turns out our atmosphere is completely teeming with RF waves. Of course, they are completely invisible to our senses under normal circumstances. If some of these radio waves are of a high enough energy level they will couple into various electrical equipment's, electronic components, and the human body itself. There are numerous cases of people picking up radio stations in their "head" without the aid of headphones. (They are actually picking the radio signal up in the metallic fillings of their teeth, or other embedded metallic objects implanted in their bodies.

Here's what's going on. Even though we are swimming in a sea of RF signals, under certain situations one or more of those signals are strong enough to convert to a hearable level of audio energy - most RF signals are not, just in special cases. Likely, if you identify the radio station and look it up, you will find it is one of unusually high power level and its transmitting facility is close to your listening location. In the two personal experiences I am thinking of, one was a 500 watt station transmitting about 5 miles from my listening location, the other was 100 watts and less than one mile away and line-of-sight to boot.

The "tuning" of the pickup circuit has very little to do with the reception phenomena you are experiencing. More so it is strictly a matter of energy levels. That is, the radio station you are receiving is simply the most powerful one in your area. If you connect a 10 foot length of wire to one terminal of your headphone jack, you will probably still pick up the same signal with and without your filter components, or actually plugging it into any of your computers ports. Also, the higher the impedance of the headphones, the better the reception. Try this to confirm what I am explaining here. Also, connect one terminal of your headphones to large metallic objects in your house, like the cabinet or frame of your refrigerator, a metallic door, window screens, or metallic exterior siding of your house. In fact, all of these metallic building components will help your computer to pick up the particular signal you are hearing.

Importantly, some element of your setup is demodulating the RF signal, which results in extracting the audio content. This can happen in numerous ways with an AM station, but far fewer with an FM station. Is the station you are hearing on the AM band? Sometimes this modulation occurs with inadvertent diode formations - as in the case of people picking up radio stations in their tooth fillings. (Diodes are natural demodulators.) In other cases the demodulation occurs from inadvertent low pass filtering and consequential energy consolidation as in your case with the headphones. Here it can be the electronic components you have added or the physical inertia of the headphone diaphragm itself. There is really no "tuning" involved as would be required in long range RF detection. Again, it is strictly a high RF energy field phenomenon.

Answer 2

If you are close to an AM radio station, the signals can be detected by any nonlinear device. This can be the microphone jack input circuitry, metal-to-body connection, metal fillings in your teeth, and many other possibilities. If the radio transmitter is strong enough (and you're close enough) you can even "slope detect" FM radio or TV audio signals with audio circuitry. Your body and the headphone wires can act as antennas.

You need strong signals to do this.

Answer 3

I have seen video signal from a TV station displayed on a TV monitor which has no tuner. I was about 1/8 mile from their antenna, which takes a lot of the mystery away.

When the signal is strong, and something can form even a really crappy diode, then you can recover AM signals.

You can recover FM as well, but you need something acting as a sharp filter. I once demonstrated a reciever for our ham club FM repeater on 446 MHz using a duplexer filter can (high Q tuned circuit) and a diode. As the FM modulation crosses the slope of the filter, it is then AM modulated by the filter, and the AM modulation is then detectable by a simple diode. A microwave diode in this case, but the point was that someone in the club had claimed it was impossible to receive audio from an FM repeater on an AM receiver. Challenge accepted.. :)