Wired News has an excellent article on GNU Radio, a software-defined radio that can emulate practically any traditional radio just by changing the software. With the right GNU Radio hardware, the same machine can act as a digital TV receiver (try forcing the Broadcast Flag down a GNU Radio owner's throat!), a satellite radio receiver, an AM/FM tuner, an analog TV receiver, and a military radar installation. All at the same time.
GNU Radio can do cool and scary stuff that old special-purpose radios can't do, like tune in and record every FM radio show, or all the cellular traffic on a certain street corner. The GNU Radio software is free software, licensed under the GPL, so you can improve on it, tweak it, start a business based on it, and torque it, all without paying anyone or asking anyone's permission.
After few minutes of normal Linux messing around ("Takes forever to boot…. Haven't got the sound driver working yet….") he turns the laptop around to reveal a set of vibrating lines in humps and dips across the screen, like a wildly shaking wireframe mountain range. "Here," he explains, "I'm grabbing FM."
"All of it?" I ask.
"All of it," he says. I'm suddenly glad the soundcard isn't working.
Radio is that bit of the electromagnetic spectrum that sits between brain waves and daylight. It's made of the same stuff that composes light, color, electrical hums, gamma radiation from atom bombs, the microwaves that reheat your pizza.
From our perspective, radio devices behave very differently — a global positioning system gadget doesn't look like a TV doesn't look like a CB set, even if they are all radios. They are single-purpose machines that use small bits of radio spectrum to do very specific tasks — about as far from the general-purpose personal computer as you can get. But there's no reason they have to be.
