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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."
Check out tapr.org and the DSP-10 project. It's a 2 meter ham radio that is defined in software, using the DSP board to handle modulation. I am saving my nickels and dimes to buy a kit, and it seems interesting. Also, since it's all defined in software, it can be connected to a transverter and the output can be SSB, FM, etc and the software for the PC can be programmed to take into account that the transverter is making the 2 meter rig into say a 10 meter or microwave rig.
-RickTheWizKid
Great! you are right on....
so where do you get DSP's that are field programmable in C?
and connect easily to a computer costing less than $200.00 in parts to cover from DC to 10Ghz?
DSP's are good for end products that are to be released to the sheep. This is better than any DSP ever created and will do it better than any DSP ever created for research and expierimentation. doing that with a DSP is near impossible for the amateur and is 100% impossible without breaking the law for poor expierimenters.
DSP's suck for research by the hobbiest..This process is best.
be sure to include the entire costs of development before offering your opinion as to weither an expensive alternative is better. (DSP's are ungodly expensive after you factor in the programming software,devkit, and required hardware all purchased legally... TI's devkit costs over $20KUSD that has all the tools available (the student kit doesnt do 1/2 of the pro devkit.)
Do not look at laser with remaining good eye.
This page has the details. Too pricey for a tinkertoy.
While TAPR has tried a lot of things, unfortunately not many of their projects have gotten off the ground since the TNC II (A packet radio modem (Terminal Node Controller) for amateur radio use.) Whatever their development process is, I think it could use an infusion of bazaar style development. They've worked on a spread spectrum radio since the early '90s. Each time they're "just a few months" from releasing a working model something changes and the project disappears again. I ended my membership after a couple of years as I just didn't see the project progressing. To be fair, it's a volunteer/hobbyist organization. Perhaps some friendly competition from GNU will spur both to release a usable product by the end of the year.
The past few years the major advancements in amateur radio digital technology have come from Europe. i.e. PacTOR, PSK31, and now MFSK. Clover was developed in the States, but being patented and other issues (leading to high prices) kept it from becoming a mainstream technology.
"Insanity is doing the same thing over again expecting a different result."
I do this for a living, and I can tell you this won't help you listen to cellular.
First, all they are doing is taking the 455kHz IF from an existing radio, digitizing it, and using the computer to do the demodulation. Thus, if your radio won't receive the cellular band, your computer won't either. And if your radio can tune into the cell band, you can listen to AMPS without a computer - it's just narrowband FM.
Now, if you are talking about GSM, PCS, CDMA, or anything other than AMPS, then you will need more than just a receiver that can tune those bands. CDMA is spread over 1.5MHz of spectrum - unless your radio has an IF that wide you are out of luck.
GSM and PCS (which is just GSM at a different frequency) is narrowband, but it's still more complicated than FM- you need to be able to receive the complex (in the a + (srqt(-1))w sense of the word) waveform, and pull the bits out of the air. Then, you need to decode the protocol, run the vocoder algorithm, and generate the audio. We use TI C6X DSPs capable of 1.6BOPS, with special opcodes to help the decoding, and Special chips to do the grunt work and it still takes a lot of work to get it to run in real time.
Now, if you are a ham, and you want to do sideband, PSK31, or other modes, this is a great thing. But don't expect to be able to monitor your neighbor's phone with it.
Besides, if you ever HAD monitored cellular, you't realize it's about as interesting as watching grass grow.
www.eFax.com are spammers
Erm. The hardware involved here isn't really general-purpose, as it requires a pretuner. (I was under the impression that 'real' software radio from the big researches pulled a few more tricks, basically creating a 'DC to light' system. Software *controlled* radios have been around for ages now; this is just a matter of decoding various modulation techniques without those stages of a regular radio set getting in the way. (e.g., if you plug an AX.25 TNC or your soundcard and appropriate software into an amateur VHF set, you will still be limited to what can be done with FM modulation. This just ties the DACs/ADCs in 'ahead of' that FM->audio hardware, and since the computer can do the same job, we can drop those stages from future radios.
The DTV (it's "Digital TV;" "High Definition" is now optional, viz. the lobbyists allowing 4 regular-resolution channels in the space of 1 analog channel, quadrupling the value of their broadcast licenses) modulation standard is known, though I can't remember exactly what they use off the top of my head. You can go out and build/buy radios that will receive the raw DTV signal right now, and even hardware to 'decode' the data stream (analog->digital). Consider that the link-layer protocol.
On top of this, the access controls for existing (subscription) digital TV services are handled through documented, but strong, cryptography. You can 'decode' (demodulate) the bitstream from the radio signal easily- nobody wants to make the radio gear expensive, it has to go into $99 set-top-boxes- but actually *decrypting* it will be another matter.
What makes DTV different is that it's a public-access system. It should be obvious that there are two possible ways DTV copy control can be handled; again, I'm not sure what they're actually doing:
1. The 'stupid' way. Include a copy control flag along with your 'cleartext' MPEG2, etc. It would be the decoder manufacturers'/coders' responsibility to adhere to the DMCA.
2. The DVD way. Create a licensing body/consortium to distribute keys to manufacturers/software developers; the MPEG stream gets transmitted encrypted, such that all licensed decoders have access to it, until a someone produces a violating one, at which point their key is pulled. This is, again, how DSS access control works, except the key is on the smartcard given to each individual subscriber; when you stop paying your bill, they take your key out of the downlink stream. (No, I'm not really sure how you encrypt one single stream for decoding by an ever-changing list of multiple keys, but that's how they do it.)
Again, all of these systems could be received by anyone with a regular radio of proper specification. Bypassing the crypto (if there is any) is the hard part. The only reason the controls will work will be because of crypto in the 'smarter' case, and because of Macrovision-style protection in the weak case (your TV card will honor the copy control bit and refuse to pass that stream to your computer; the manufacturers will build this way because they don't want to be DMCAed). If the weak case is the one they go with, then you can just plug a regular radio to your computer and ignore those no-copy flags- all having the 'software' radio does is make it easier to demodulate acronyms other than FM or AM, but *radios exist that can do this already.* They're just kinda expensive, complicated beasts for enthusiasts ($1,000 Yaesu/Ten-Tec/Kenwood/whoever) vs. what could soon become a $20 ADC and a $5 tuner.
My notion of GNU Radio would be simple and inexpensive free FM BROADCASTING. Of course, the FCC has issues with that... if you pay attention to the micropower FM scene, it's actually quite similar to what GNU stands for. It's about empowering people.
The catch is, it's pretty easy to screw up an adjacent station if your signal is screwy and out of spec.
The low-power FM movement is worth your attention- if you're even reading this article you probably 'get' the importance of micro/local broadcasting. It should come as no surprise that corporate radio has been using Congress and the government to try to stamp out even the possibility of people using local FM broadcasting to provide alternatives- it mirrors what other content industries have been doing with more Slashdot attention. In December 2000 Congress passed an appropriations bill with a rider that was snuck in to halve the number of low power FM licenses the FCC could legally issue. Not only was corporate radio behind this- NPR also supported the illegalization of low power FM broadcasting. McCain (R-AZ) has introduced a bill to counter this and support low power FM again. Furthermore, on February 8, 2002, the Court Of Appeals struck down language in this anti-LPFM act which had prohibited the FCC from issuing a license to anyone who had ever previously been involved with pirate radio. The court held that this was unconstitutional. (funny how both in the judiciary and Congress, these guys are forced to deal with all types of injustice and power grabs, not just the sorts that are close to the hearts of Slashdotters ;) )
These people are the other side of the coin: transmitters from microwatt to 500 watts and kits for all kinds of nifty things like subcarrier decoders, shortwave, the aviation band etc. I don't know anything about them but their catalog but it would make any true geek absolutely drool, with all the build-it-yourself devices to do arcane and amusing things, and the flashy computerised rackmountable transmitters. Too cool.
Jack,
You're right. The alpha HW includes an inexpensive downconverter (about $35. in small to moderate volumes) which can be tuned by the PC from 50-860 MHz. It has an IF bandwidth of about 6 MHz (matching a NTSC video channel) and the model we are using offers its IF at just above DC to 6 MHz.
The GnuRadio host SW can process narrow and wideband signals falling within this 6 MHz chunk of spectrum. It can even process several signals simultaneously.
While the Maxim part is fast, its not very sensitive. 8-bits of accuracy is way too small for wireless. The lowest useful bit depth is about 12-bits, 14 would be nice.
a dc_perf ormance_11_08_00.pdf
See
http://www.sdrforum.org/MTGS/mtg_21_nov00/
The DSP-10 is a cool project. Some of the things that distinguish GNU Radio from it is our preference for a *much* wider IF bandwidth, and our use of conventional CPUs instead of DSPs. The vast majority of our code is in C++, versus Analog Devices 21xx DSP assembler.