It happened quite a few years ago, but I distinctly remember a moment that occured late at night when my computer, specifically the components within the tower case (no speakers were hooked up) suddenly started broadcasting a transmission from a trucker’s CB radio. Needless to say, it freaked me out to no end for a while, but then a nagging thought in the back of my head told me that I had actually heard of this phenomenon occuring before. Does anyone have any information, or know of a website, that deals with the phenomenon of electronics spontaneously resonating radio signals? I’m pretty sure I didn’t imagine it!
I’m sure you didn’t imagine it. The phenomenon is quite common, and not just limited to CB transmitters - you can get this kind of interference from regular radio transmissions, pagers, and other sources as well.
Unfortunately, CB radios are notorious for it. Many CB operators use “boots”, linear transformers that boost their output for longer range. But since the system isn’t tuned carefully, these higher-power transmissions tend to splash into all kinds of electronics and cause interference. Even a regular-powered CB radio with a poorly-tuned antenna will generate interference - and most CB operators have no idea of how to tune their antenna (Standing Wave Ratio, or SWR) for optimum performance and minimum interference.
I suspect that what you heard from your tower case was interference through the built-in speaker. Even without external speakers, all CPUs that I have torn apart have had a built-in, which generates the various beeps and boops that you hear at startup.
It’s very easy to “accidentally” make a radio receiver out of electronic components. If you want to make a quick and dirty AM radio receiver, all you need is a tuned antenna, a rectifier, and a filter. Soldiers in WWII used to make them out of bits of wire and a razor blade (google “fox hole radio” for more details). A “wall wart” (those typical little power supplies that have a box that plus into the wall and a cord which plugs into your CD player, computer speakers, etc) is typically just a transformer, a diode, and a capacitor. The diode is a rectifier and the capacitor is a filter. It’s an ideal AM radio receiver. All over the inside of your computer (and your stereo, and TV, and most other electronic devices) you have naturally occuring AM radio receivers, formed by the various bits of wire and circuit traces acting as antennas, integrated circuits acting as rectifiers, and other bits acting as filters. In fact, it turns out that if you are fairly careless in how you design things, you are very likely to make an accidental radio receiver out of it. Something as simple as a long piece of wire going into an amplifier circuit makes an excellent radio receiver. Amplified computer speakers are notorious radio receivers, especially the cheaper ones. The speakers will chirp and beep whenever a cell phone is nearby, and may pick up radio and TV audio signals from all over the place.
There are two speakers inside most systems. The first is the cheap piece of crap PC speaker left over from the old 8086 computer days. Sometimes this is built onto the motherboard so that it will beep when the motherboard starts up, so you may not even need a seperate speaker hooked up to your motherboard. The second speaker is on your modem, if you happen to have one, so that it can make those annoying squeaks and squawks that are only useful to technical geeks when they try and figure out why a modem isn’t connecting properly. I suspect that for the OP, one of these speakers was accidentally being driven by the CB radio.
It is possible to accidentally make a speaker too, since all you need is something that will vibrate when electricity passes through it. That humming sound from electrical transformers doesn’t come from a speaker. It’s just coils of wire vibrating.