Universal Radio Grabber: the USRP

Nethemas the Great writes "The Universal Software Radio Peripheral or USRP created by Matt Ettus and Eric Blossom gives a new perspective on the radio spectrum, as in just about all of it from DC to 2.9Ghz. With the right software and daughterboards, their USRPs can capture FM, read GPS, decode HDTV, transmit over emergency bands, track peoples movement via their mobile phones, and much, much more. With prices starting at just $550 this new toy is accessible by most anyone."

Comments

The real question

[Umbral Blot]

The real question: how long before it becomes illegal to own or use one?

Re:The real question

[zippthorne]

Transmitters must be licensed. Even your 49 mhz walkie-talkie is licensed. It's not licensed to you specifically, it's type accepted, so the manufacturer can sell lots of them. If you were to modify it to transmit on another frequency, you would have an unlicensed transmitter and therefore subject to prosecution if you actually used it.

It makes sense to license transmitters. The EM spectrum of useful radio frequencies has finite bandwidth, and we must have some plan for use so that the most people can get the most benefit out of it. This includes astronomers, hobbyiests, emergency services, cell-phone users, television studios, and many more. Licensing solves the traffic jam problem.

It makes much less sense to license receivers. The radiation is there, passing through people, even. Frankly, I don't understand why anyone would think that I don't have the right to intercept any signal which passes through my personal space and process it however i please.

But that seems to be the case. Recievers capable of recieving cell-phone frequencies may not be sold. I am unsure of the legality of modifying or building your own equipment for that purpose, but I am sure the cell-phone companies have lobbied hard to make that illegal as well. As a longtime desirerer of encrypted cell-phones, it has frustrated me that they want to transmit "in the clear" and just make it a crime to recieve, especially as equipment from before there were cellphones exists that has no hardware blocks on those frequencies whatsoever. Fortunately, CDMA forces at least a rudimentary level of quasi-encryption.

Re:The real question

[egomaniac]

It makes much less sense to license receivers. The radiation is there, passing through people, even. Frankly, I don't understand why anyone would think that I don't have the right to intercept any signal which passes through my personal space and process it however i please.

So it should be legal for me to use a night-vision scope to look into my neighbor's bedroom window at night? After all, her naked body is reflecting electromagnetic radiation into my personal space. Amplifying it into a visible image, digitizing it, and making it available on the Internet seems like a perfectly logical step, doesn't it?

People have an expectation of privacy. They expect you won't be sneaking around peering into their windows at night, and they expect you won't be intercepting and decoding their personal telephone calls. Yes, you have the right to decode electromagnetic radiation. And yes, the callers have a right to privacy. Any time two different rights conflict, one or the other has to take precedence. Privacy is a much more desirable-to-society right than is the ability to spy on our neighbors, and so privacy wins.

Homebrew SETI?

[superdan2k]

Imagine a not-quite-Beowulf cluster of these -- your own homebrewed VLA. It'll receive in the "waterhole band", and VLBI ain't too hard to figure out. Set up enough ground stations and switch between them as-needed to compensate for what you're viewing and the rotation of the Earth, and you've got a fulltime radio telescope with a dish effectively as large as the earth, whenever you want it...

Open source radio astronomy anyone?

"the right daughterboards"

[Erandir]

Be careful of that seemingly innocuous qualification: "with the right software and daughterboards"... both imply serious limitations to the technology.

Firstly, the "right" software: Even with a reasonably fast processor (say 3 GHz) today, you are typically only be able to process, at most, a few million samples per second -- especially if you are performing complicated modulation/demodulation, coding/decoding, filtering and protocol processing. Each sample may require substantial computation, and that limits the number of samples you can process per second. That, in its turn, affects the bandwidth that a processor can address (i.e. how wide a part of the radio spectrum you can "see" at any one time).

Secondly, the "right" daughterboards: To be able to address a wide bandwidth, we require digital-to-analog and analog-to-digital converters with high sampling rates. These are limited by the state of the art in signal conversion technology -- typically a couple of million samples per second if we want a reasonable number of bits per sample (at a reasonable price). Push it beyond that, and we have to be happy with fewer bits per sample (may 10 or 8 bits). This introduces noisiness to the signals being transmitted or received, degrading the fidelity of the software-defined radio.

Also, a daugterboard usually has some form of signal translation hardware ("mixers") to translate the low-frequency signals that computers can generate to and from the higher parts of the radio spectrum. Although broadband mixers are available, they need tunable oscillators (reference frequencies), and these tend to be limited to narrower parts of the spectrum. Also, analogue filters, amplifiers and antennas (which all form part of a typical software radio front-end), usually are limited to specific ranges of the radio spectrum.

In short, software radio daughterboards tend to be fairly application-specific (or at least spectrum-specific). We can do a lot of things in software, but a "universal" software radio needs a lot of hardware swapping. I think that makes it a bit less "universal". It might also push the cost of a truly multi-purpose system quite a bit beyond $550.

But I'm glad to see this technology receiving such mainstream attention, and I applaud the efforts of the designers. I just think that TFA (and the post) could maybe be a bit less sensasionalist.

And yes, IAASDRE.

G-J

Re:I hear hype...

[lowen]

I have two of these personally. At PARI we have four of them. They work. And work well, for radio astronomy.

As to capturing the entire FM band at one fell swoop, I know for a fact that the USRP and a good USB 2.0 High-Speed host can sustain 32MB/s transfers. This becomes an actual sampling rate of 8MS/s in quadrature, which means a full 8MHz band can be sampled at 12 bit precision. The FM band is 107.9-87.9=10MHz wide. At 12 bits, no, you can't get the whole band in. However, the USRP can go 16MS/s at 8 bits (again, in quadrature, which effectively doubles the sample rate), and consume 32MB/s across the USB. Since FM (frequency modulation) doesn't require large dynamic range in terms of bit depth, it is possible that you could get nearly full fidelity audio out of all FM channels simultaneously: but you would need one big honking PC to demodulate in real-time.

As I am a licensed Amateur, I can use this as a transmitter, in the bands and with the modulations to which my license class is allowed. I have the 400-500MHz transciever board; I am of course limited to the 70cm Ham band for transmission, and I of course honor that. It works quite well.

For radio astronomy, I have the DBS_RX board, and it directly tunes several radio astronomy bands, including the Hydrogen line at 1.42GHz. It works quite well for both continuum and spectrum studies, although I still have some bugs (with considerable help for the GNUradio project and other programmers) to work out.

Re:decoding HDTV?

[TheRaven64]

The Slashdot summary was monumentally bad. My first thought on reading it was 'this sounds like the kind of thing you could use with GNU Radio." Clicking on TFA, I discovered GNU Radio was in the article title. Strange how Slashdot, usually GNU-obsessed, would miss that out.

GNU Radio is a pretty amazing piece of software. I attended a talk about it at Linux '05, and was amazed by the capabilities. When they say they are decoding HDTV, they mean that they are doing it in software. All of it. Not just decoding the MPEG-2 streams, but everything this side of the analogue to digital convertor. They are not running it through a decoder box and grabbing it from a FireWire connection, they are capturing the radio signals, converting them into digital signals in hardware and then doing everything else in software.

The basic architecture of GNU Radio is a filter API. Individual filters are written in C++ for performance and then they can be joined together and controlled with Python, making the barrier to entry very low for anyone who wants to tinker with it. Don't be fooled into thinking you need an expensive receiver like the one in TFA to play with it either, it will accept input from a large number of ADCs, including sound cards. You can use it to apply transformations to any digital waveforms.

You can use it to implement something like 802.11 entirely in software, generate telephone dialling tones on your sound card, modulate your voice to sound like a Dalek, decode HDTV signals, or a huge range of other things. It turns your PC into a hugely powerful programmable DSP.

The hardware in TFA is just icing on the cake. As I recall, the specs for a slightly simpler model are available from the GNU Radio site, so you can build one yourself if you have (a lot) more time than money.

Re:Depends on the country

[mindriot]

This product seems to receive the entire spectrum by default.

No. The USRP motherboard is capable of handling anything from DC to 2.9 GHz, but you need the matching daughterboards for specific ranges. Daughterboards include:

• BasicRX, 0.1-300 MHz receive
• BasicTX, 0.1-200 MHz transmit
• LFRX, DC-30 MHz receive
• LFTX, DC-30 MHz transmit
• TVRX, 50-860 MHz receive
• DBSRX, 800-2400 MHz receive
• RFX400, 400-500 MHz Transceiver
• RFX900, 800-1000 MHz Transceiver
• RFX1200, 1150-1400 MHz Transceiver
• RFX1800, 1500-2100 MHz Transceiver
• RFX2400, 2250-2900 MHz Transceiver

Also, you obviously need to have the matching antenna to actually receive something useful in a given frequency range.

Now, whether or not receiving particular frequencies is allowed or not will obviously depend on the FCC and similar regulatory organizations (in most, if not all countries, for instance, receiving police radio frquencies is illegal). Maybe the FCC regulation you mentioned is taking things a bit too far... cell phone standards like GSM are encrypted anyway (unless, of course, you go for a man in the middle attack).

As to your FCC quote, I suppose the question is whether being able to buy another daughterboard/antenna means it can be "readily altered to receive such frequencies." With respect to transmitting, the FAQ states that since it's sold as test equipment, you don't need a license. I wonder if the "test equipment" status supersedes that FCC statement as well?