GNU Radio

Max Hyre writes "Apropos (!= man -k :-) RIAA, web radio, and other such data-dispersal disagreements, here's a new way to do it your way: a fully software-driven radio receiver; just strap some off-the-shelf DAC hardware into a generic computer, and let the software do the rest. While I can just barely spell `sideband', this looks like it could be more fun than any set you ever had before, especially after those in the know build up some kewl apps for the great unwashed like me. They're also dreaming of GPS, cellular phones, &c.. My only gripe is that the web pages proper don't seem to have any cookbook recipes for the hardware; maybe that's in the docs with the source, or maybe this is strictly for the experienced, for now."

Comments

The forbidden fruits of radio

[Anonymous Coward]

We could have all those bands again that they banned; the 800mhz AMPS area, HDTV, anything just pumped into our boxen.

Re:The forbidden fruits of radio

[gbnewby]

In the US, radio receivers and scanners are forbidden from receiving in the cellular phone bands (not that hard to get around by buying a radio elsewhere or modifying your own).

Spread-spectrum technology, as used in wireless phones, especially 3G wireless and other communication, is generally inaccessible to your generic home scanner or ham setup. Also, it's often digital, which again means a home scanner or ham is out of luck.

Enter GNU radio. This sounds like it will easily enable receiving the "forbidden" bands, and give a lot of computer power to re-assemble the spread-spectrum signals. I don't know if this is the intent of the developers, but the potential for bypassing existing radio "security" (really, security through obscurity & legalese) seems strong.

Re:The forbidden fruits of radio

[Anonymous Coward]

Try security through RSA *plus* what amounts to a cryptologically proven shared-secret technique of frequency hopping in the case of CDMA. (The shared secret, actually the seed for the frequency-hopping algorithm, is hardcoded into the phone; it is not exchanged over the air at all.)

Cordless phones and analog cellular have neither of these protections; if the cheap 2.4GHz phones do any frequency-hopping at all, the same random seed is likely used among all units of the same model. Analog cellular really only frequency-changes when switching cells; that's why a good CDMA-based digital system is often more robust even when the analog handsets are pushing a much, much stronger signal by any measure.

Yes, you could easily listen to analog conversations; you can already do that easily. However, if you capture a *TDMA* (GSM) conversation (no shared secret there), you will still need to crack the encryption used, likely not a realtime operation with a desktop PC, although I believe there was a big weakness in the pre-3G implementation. With CDMA, you have to discover the seed value for a particular handset, and *then* crack the crypto.

Of course, there may still be weaknesses or backdoors in these modern implementations, and more widely-available equipment means they're more likely to be discovered. It's still wrong to claim no real protections have been introduced at all.

Given that cellular test equipment can still be marketed, I'm not sure what the equipment-sale restrictions really forbid. However, if this does become a popular way to eavesdrop on older cellular networks, you can bet that 800-900MHz-capable pretuners will be mandated off the market.

20M samples/s ADC to receive 95MHz FM?

[r6144]

Does the ADC mix down the frequency prior to A/D conversion?

Re:Cool, but pointless

[TooTallFourThinking]

I don't think they are marketing it as a replacement for a DSP. Clearly if you wanted to do something like this as efficient as possible, a DSP is the way to go. You don't slow do your computer with all this additional processing - unless you've got a disgustingly fact computer ;).

But at the same time, those who can't afford the $500+ DSP kits to start playing around with, or those who want to see what are the limits they can push with their computer, this sort of stuff it probably right up their alley. I kind of dig it.

As long as everyone understands the differences between the two approaches, everything is cool. This gives more people the opportunity to play and I am all for that.

-Greg

Multiple channels

[Animats]

Software radios can receive multiple channels at once, provided enough compute power is available. Cell sites use this to receive hundreds of channels without having hundreds of separate receivers.

This has some possibilities. One is a radio that listens to the entire FM band and, quickly and automatically, builds an MP3 music library of popular music. Legal, too. (Audio Home Recording Act)

Add-ons to this project could include automatic song identification (there are song-signature databases for this), use of multiple copies to recognize and remove announcer blithering, and intelligent audio cleanup from multiple copies.

Great open-source project for audio people. Nice device for cars, too.