My speakers have been labouring in a pretty sorry state for the past few months. They refuse to emit any sound unless a pair of headphones are plugged in, and lately I’ve had to leave the jack-plug hanging precariously from the mouth of the socket in order to elicit any sound at all. It wasn’t an ideal situation, but it worked.
Until lastnight when I plugged them in and I started receiving crystal-clear reception of great classic rock from the 60’s, 70’s and 80’s.
How did this happen?
It’s somethinig that happened a lot more often in the 70’s and 80’s with the transitor electronics. You could have it happen on a cassette recorder when playing back or recording. Local radio stations with relative high power output will be the culprit. The heart of a radio uses a diode to pick up a radio signal, and a transistor can be used in it’s place. The stronger the signal the less descriminating the components need to be. Electronics are full of components able to act a s a signal reciever, and it’s beyond my ability to explain it in detail anymore, becuase of the if you don’t use it you lose it principal. Unless you want to learn electronics, I don’t know how much somebody explaining in detail will help. I’m sure somebody can explain it better than I, so maybe they can take over.
I am thrilled that someone has said that there is a reasonable explanation for this.
When I was a freshman in college, I had an old boomboxy thing. It started picking up the campus radio station, whether you were playing the radio or not. Playing a CD? Campus radio station in the background, softly. No problem, right? I just turned the CD up. Unfortunately, it just got louder and louder, and the problem became so bad that you couldn’t ever play anything but the campus radio station, at varying levels of Very Loud. Frankly, it wasn’t that great a station. I ditched the thing and got a new stereo, which worked fine.
Everyone I have ever told this to has either accused me outright of making it up, or nodded and then walked away very fast.
I admit to not fully understanding the explanation offered, but I get the basic idea. And I am happy that an explanation has been offered at all. 
I’ve had this happen to me before. My old set of computer speakers would pick up AM radio and sometimes intercept my neighbors’ phone calls. I assume it’s something that really low-grade electronics equipment does when it ages. FWIW, it was a set of Cambridge Soundworks PC speakers and they only started doing it after I’d had them for 7 or 8 years.
Are you from Winnipeg, Manitoba, by any chance? Whenever I go back home there to visit, my parents’ computer will frequently pick up the local classic rock station, CITI-FM. Given that it used to be the most powerful FM station on the planet, this isn’t entirely surprising, but it’s still a little annoying.
All I can contribute – lacking any useful knowledge as to why – is another anecdote or two.
In the case I can vouch for as real, I had a record player that was just a record player, no radio. It was a plug-in type, no batteries. It only played LP’s and 45’s, long before tapes and CD’s were even available. There was one outlet in the building, in a vacant apartment at that, where I could plug this thing in and pick up a specific (always the same) local radio station. I forget whether it was AM or FM. If I moved the record player to another outlet, the problem went away. In my limited knowledge of how these things work, I attributed it to the wiring in the building coupled with the electronics in the record player.
The other anecdote which I have only heard about, never experienced it first hand, is that there are some people who can pick up radio signals with their teeth. I have no idea how that would work, nor even if such stories have any truth to them.
Any piece of wire is capable of having an electrical current induced in it, and this is how an antenna works.
If the signal strentgh is sufficiently large, then it follows that a larger current is induced into the wire.
The size of incduced current depends on certain factors, one of course I have just mentioned, but also the frequency of the signal is important, and the length of the wire, basically we look at a signal frequency in terms of wavelength.
If you couple up a transmitted signal with particular frequency, with a length of wire whose length is a particular proportion of the wavelength of that signal, then the induced current will be larger.Which is why you might hear of terms such as quarter length antenna.
All this actually means is that to recieve a signal, you need a transmitter, and a piece of wire.
Next, to actually transmit a signal, the frequency of the signal itself has to be very much higher than the range of the human ear, in the order of thousands of times higher, but also up to the millions, or beyond.
If we want to transmit information in the human hearing range, we have to encode it into the transmitted signal, there are several ways of doing this, including digital packets, or varying the frequency of the transmitted signal in sympathy with the information we wish to hear - this is called frequency modulation.
In the case of the OP, the method of encoding a lower frequency signal, such as music, onto a much higher frequency - (which we call the carrier signal), what we do is vary the size, or power of the carrier signal and use our information to actually do the varying. This is called Amplitude Modulation - AM and is almost certainly the culprit in this case.
Once you have encoded your signal, and transmitted it, and then recieved it, you then have to decode it.
It really does not matter what particular transmission system you use, it must be decoded somehow.
AM signals are very simple signals compared to other methods of transmission, and so the decoder is also very simple.
This can be in its simplect form, a diode which rectifies the the positive and negative vibrations of the high frequency signal, which then goes into something that has a tendency to average out the result.
It happens that a diode is capable of doing both of these fucnctions, and specialist diodes are made to exploit this dual ability.
A diode is generally thought of as a specialist electronic component, and an averaging device might also be considered to be another component, the Capacitor.
Actually, you do not need high tech manufacturing processes to accidently produce a diode.
If you have two dissimilar materials touching each other, and both of them are capable of allowing electrical current to flow through them, there will be a tendency for current to pass through the junction between the two parts better in one direction than the other- usually this differance only amounts to a few thousandths of a volt and is often hardly noticeable, but occasionally things work out differantly.
This can happen especially when there is a certain amount of oxidation between materials.
In such cases, the differances between sending current one way, compared to sending it the other, can amount to a couple of tenths of a volt.
Now the voltage induced by the recieved current in piece of wire may be in the order of millionths of a volt, so as far as the signal is concerned, ever a poor rectifier of one tenth of a volt, is quite a barrier in one direction, and this junction is a diode.
All we now need for you to hear the result is some form of amplifier that is somehow connected to one side of that diode, it could be almost any electronic device, and often not what you might expect.
Following up on casdave’s post, “crystal radio” kits used to be popular among scientifically bent kids when I was growing up in the 1960s; maybe they still are. It’s fascinating that the radio waves are just “there”, and with the the right kind of equipment you can just pick it up without any battery or other power supply. I remember having one in my room that used the window screen as an antenna.
I used to live not far from the KDAY transmitter in Los Angeles, and the station was often picked up on standard telephones in the neighborhood. The installers routinely put a resistor across some internal terminals to minimize this problem.
You’re lucky that you are picking up a rock station. My computer speakers and one of our TVs pick up the local Christian music station. My son will be playing Call of Duty 3 and underneath the sounds of bullets, explosions and destruction you can faintly hear people singing about Jesus, salvation and love.
Is there some way to “shield” the items from these extraneous signals?
Any sort of metal box surrounding the speaker and the wire should work. Tin foil is probably the easiest do it your self way.
Dude that is so perfect as a background for those sniper missions, that is if you have seen “Saving private Ryan”
I used to work near a Naval Air Station and my computer speakers would sometimes pick up radio conversations from the pilots/tower.
Now that this has progressed a little further, I want to add that this is why I hate all these people claiming to record dead people in a graveyard. It’s errent broadcasts people.