Strange Signals

It’s Friday nite. Once every two weeks I take the accumulation of bottles and cans off for redemption. The Nutmeg State has a 10 cent deposit on most recyclable containers. That makes it worth keeping them in a separate receptable until I get 10 or 20 bucks worth of them. Then after dinner every other Friday I drive up the supermarket where they have a redemption center. There’s a Goodwill across the street, and more often than not I find a decent book or interesting item there. Been only books as of late, but that’s another story.

It’s after dark when I head out. The car radio is listening to an AM station TK miles away in Canada. It’s one of my faves. Reception isn’t perfect; doesn’t have to be. People complain about the noise on the AM band, I find it comforting. And useful. Learned that cop cars are electromagnetically noisy, especially on the lower frequencies. A standard car radio tuned the AM band can pick up that noise starting about 200 or so feet away. Useful thing to know, and needs further experimentation.

You’ll also hear noise from other things, like neon signs and industrial microcontrollers. Range is about the same, maybe a little shorter. Those are the signals you can identify. You look around, see a neon sign, noise level drops the farther away you are from the sign. Or a flashing traffic light controller is causing your radio to buzz in time with the light flashes. Perfectly normal and repeatable.

Then there’s the other stuff…

You’ll be driving down the middle of nowhere, radio on the AM band. You’ll catch some interference, and listen. The signal sounds like data. Probably is, from something. The fast switching 1s and 0s in a computer generate RF noise, and with the right equipment and technique you can figure out the 1s and 0s mean. Uncle Sam called it TEMPEST. That much is known.

Here is where things get interesting. Sometimes you’re driving down the road, pick up some “interference”, and not be able to locate it. Something is making the noise, but you can’t trace it to a programmable Christmas light display, a neon sign, or the cop car parked on the side of the road with the officer inside surfing porn on his mobile data terminal.

As we continue to become more digital, we can expect to get more interference from what the FCC calls unintentional radiators. Some of them you’ll be able to identify. Others…

You can make a whole hobby out of finding that sort of thing.