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Software-Defined Radio For $11

Posted by timothy on from the us-dollars-of-course dept.

Malvineous writes "Don't have $1500 to drop on a USRP? A Linux kernel developer has discovered that a Realtek digital TV tuner chip has an undocumented mode that turns it into a software-defined radio, with a frequency range of 64-1700MHz. The going rate for one of these USB devices can be as low as US$11. If you're unfamiliar with software-defined radio and have 20 minutes to spare, Balint Seeber has a great video introduction."

11 of 171 comments (clear)

  1. Too long by ebcdic · · Score: 5, Insightful

    I'm unfamiliar with software-defined radio, and I don't want to spent 20 minutes watching a video. I hate this trend of using a video for something that could be explained in text that I could read in a fraction of the time.

    1. Re:Too long by Auroch · · Score: 5, Insightful

      Actually, I think the point the OP was trying to make was something like ... "Why not just explain it in a sentence or two IN THE F*SKING ARTICLE instead of linking a video or an external source".

      --
      Quartz Extreme and Core Image. Are there any other real reasons to spend all that money on generic hardware?
    2. Re:Too long by bmo · · Score: 5, Interesting

      Software defined radio has the government worried and paralyzed. The government is used to individually regulating the frequencies and power levels and signal characteristics of each kind of radio-using device. An AM/FM radio specifically does not pick up police or cell phone frequencies, and things like CBs and walkie-talkies and cellphones and baby monitors all have specific power levels and specific frequencies they can broadcast on, and they only broadcast in specific radio formats. And those limits are hard-baked into the devices by their exact circuitry. Software defined radio throws that entire idea out the window. A software defined radio is going to have some inherent power limit based on the exact hardware, and some minimum and maximum frequency range based on the hardware, but generally it can handle a very broad range from low frequency bands to high frequency bands, and they can send/detect absolutely any radio format over that entire range, and they can do it at full power. There's no way to regulate "don't detect police/cell frequencies", and no way to regulate "don't broadcast FM on what is supposed to be an AM band", and there is no way to regulate different power levels on different bands. Once you sell a software defined radio, the end user can load in any software they want.

      Anyone with the technical knowledge can do any of these tasks in hardware, for not a lot of money. There are entire libraries of books and technical articles on how to broadcast/receive on any band, even "forbidden" ones like 800MHz cellular. I remember an article in Popular Communications for a down-converter you could build to listen to 800MHz back in the early 90s that simply screwed into the BNC of your scanner in line with the antenna.

      BFD.

      >implying it's somehow illegal to listen to bands outside of AM/FM

      What the hell are you talking about? Beyond the Cellular legislation, any and all bands are open for reception. It's your right to intercept radio waves on whatever spectrum and you don't need a license to do so. You only need a license to transmit on licensed spectrum.

      >cannot regulate power levels and bands

      As if they weren't able to regulate for the past 80 years?

      Protip: If you are transmitting 1kw, and transmitting in a band you shouldn't be in, it won't be the feds who track you down, it will be the licensed operators who will find you and turn your ass in to the feds and they'll be happy to do so.

      The only reason why Joe Trucker doesn't get turned in with his 1kw linear on CB is because he's a moving target. Anyone else sitting in his basement throwing shitty harmonics up and down the bands can be found.

      Also, software defined radios are not amplifiers. You are conflating one technology with another.

      The amount of wrong in your post is staggering.

      --
      BMO

    3. Re:Too long by Anonymous Coward · · Score: 5, Interesting

      What the hell are you talking about?

      1) The hard bit of any radio, especially important for transmission, is low noise band filtering, precise tuning and mixing to convert to/from AF. This all involves a lot of careful analog design and cannot be replaced by the S of SDR. Sure, the oscillator can use DDS, but that's not going to be done by wasting your computer's CPU cycles and it wouldn't make any difference anyway;

      2) For analog modes, it's arguably easier to build a circuit than write decoding software. For digital modes, you're either running software on your desktop/laptop or you're running software on the radio's CPU. The only relevant questions are a) whether the modulation is documented - the answer is usually "yes" except for military; b) the keys for any encryption are available to you - if not, being able to implement an SDR makes not a hoot of difference;

      3) Yes, you can do some fine DSP with a modern CPU but only an idiot thinks this is a substitute for a good antenna and (per 1) front-end.

      SDR is the e-m equivalent of the "winmodem" in dial-up days: yes, you have the opportunity for a lot more versatility, but only by creating something dumb and offloading the work to a less power-efficient general purpose computer which may or may not have something better to do.

    4. Re:Too long by girlintraining · · Score: 5, Interesting

      The only reason why Joe Trucker doesn't get turned in with his 1kw linear on CB is because he's a moving target

      Actually, it's because the government just doesn't give a sh*t about CB radio frequencies. But given that it uses an incredibly simple modulation scheme, it can easily be traced and tracked in realtime. All you need to catch "Joe Trucker" is three antennas spaced one wavelength or more apart and you can get a fix on their position. They may be a moving target, but they're moving along a fixed path: The road. Find a guy heading northwest in the same direction as the highway and you just hop on the road a few exits up and join the flow of traffic. He'll talk again, and when he does... oh look, it's the guy 50 feet in front of you in the left lane... *flips on lights* Goodbye 1kW transmitter, goodbye trucker.

      Be more concerned about frequency hopping mobile devices that use a PRNG to communicate with another device over a range of frequencies and encoding techniques... That requires a LOT more equipment to sort out where the signal is coming from. Actually, that's pretty much what the military does... o_o

      --
      #fuckbeta #iamslashdot #dicemustdie
  2. Some info from the page by Nyder · · Score: 5, Informative

    rtl-sdr

    DVB-T sticks based on the Realtek RTL2832U can be used as a cheap SDR, since the chip allows transferring the raw I/Q samples to the host, which is officially used for DAB/DAB+/FM demodulation. The possibility of this has been discovered by the V4L/DVB kernel developer Antti Palosaari.
    Specifications

    The RTL2832U outputs 8-bit I/Q-samples, and the highest theoretically possible sample-rate is 3.2 MS/s, however, the highest sample-rate without lost samples that has been tested so far is 2.8 MS/s. The frequency range is highly dependent of the used tuner, sticks that use the Elonics E4000 offer the best range (64 - 1700 MHz).
    Supported Hardware

    So far, the following devices are supported:

            ezcap EzTV668 USB 2.0 DVB-T/DAB/FM stick (Elonics E4000 tuner) (sources: AliExpress, Dealextreme)
            ezcap EzTV666 USB 2.0 DVB-T/DAB/FM stick (Elonics E4000 tuner, picture Download)
            Hama nano DVB-T stick (Elonics E4000 tuner)
            Terratec NOXON DAB/DAB+ USB-Stick (Fitipower FC0013 tuner)

    People over at reddit are collecting a list of other devices that are compatible.

    Other sticks based on the RTL2832U might be added in the future as well.

    --
    Be seeing you...
  3. Not Searchable. by solios · · Score: 5, Insightful

    Time isn't the issue for me. The issue for me is the fact that video "tutorials" feature voices that frequently grate on my nerves. Worse, the video tutorial cannot be quickly searched for the relevant information.

    Seriously. I can find out if a text tutorial is relevant to the issue at hand in seconds. With video tutorials, I've typically closed the tab before the "host" finishes talking about how great he is, how great the software is, and what the tutorial is going to cover.

  4. Re:better get by Anonymous Coward · · Score: 5, Insightful

    Don't be a retard.

    It's a TV receiver, it has no transmit capability. No FCC license is required to receive (almost) anything with a Class 15 device, which these are. The exception would be cellular telephony, but AFAIK there is no FCC license permitting eavesdropping on those -- you're either the (licensed) carrier who's actually handling the call, or you can't listen.

    If you add a transmitter, well, the fact that you're listening via TV dongle obviously doesn't eliminate the licensing and equipment requirements for whatever radio service you're operating in, so a warning specific to this case is unneeded. Anyone "freebanding" or otherwise operating illegally probably knows exactly what they're doing, and if they don't care about what the law says, I very much doubt they care what you say either.

  5. Challenge Accepted by Gordonjcp · · Score: 5, Informative

    In a conventional radio receiver, you start by filtering off the wanted signal with a broad filter, mixing it with another locally-generated signal (the Local Oscillator) to make a lower Intermediate Frequency (IF), then filtering the IF to extract a single "channel" of information. Then you demodulate this, possibly after mixing it down to an even lower IF.

    In a software-defined radio, you convert directly down to a much lower frequency (audio frequency, even), but - and this is the clever bit - you do it with two local oscillators, 90 degrees out of phase. This gives you a complex sample, a pair of samples representing In-phase and Quadrature, or the real and imaginary components of your signal.

    From there you can apply digital signal processing techniques to extract the wanted signal, show an FFT of the chunk of band you're capturing, and so on. This lets you do very sharp filtering, because you're no longer constrained by the physical realities of trying to implement electronic filters with practical components.

    Shameless plug - if you want to try SDR out, go here:
    https://github.com/gordonjcp/lysdr
    Follow the instructions in the README, then either post a reply or bug me in irc.freenode.net ##electronics for further instructions.

  6. Been there, done that by ctrl-alt-canc · · Score: 5, Informative

    A few years ago, together with a friend, we reverse engineered a DVB-T usb pen by Hauppauge, and we were able to extract the raw data stream skipping the demodulation process. We did it since we wanted to test if it the device could be used as a DSP IF strip in a homemade spectrum analyzer. The device worked, but the analog IF strip we wanted to replace was actually drawing circles around its digital replacement, so we abandoned the project. 8 bit of resolution and an hardware designed for a very specific purpose couldn't bring us too far, as we feared.
    It is nice to see that somebody else was capable to reverse engineer these devices, but as you can see from their results, they aren't actually that good. I saw somewhere that a USB pen for DVB had to hit the market, and its ADC has been announced to be 12 bit wide.This could be an interesting device to hack for SDR applications, hoping it isn't vaporware...

  7. Re:knowing he did that with an 11 dollar TV card by Anonymous Coward · · Score: 5, Informative

    You realize that if a significantly-sized company is selling you a radio for $1K that has $150 worth of parts in it, for an item that isn't mass-market consumer
        (and ICOM/Kenwood/Yaesu radios intended for the HAM market aren't "mass market", compared to, for example, cell phones), that they are on the edge of
        *losing money*. I've run two different manufacturing businesses in the last 20 years, and really, if you only look at the raw BOM costs of something, and don't
        factor in all the other costs of bringing a reliable product to market, you'll go out of business.

    Many of the so-called "high dollar" SDRs out there are "high dollar" for fairly good reasons. They are typically sold into markets where economies of manufacturing scale don't really apply, they often have feature sets that are *vastly* larger than what we're seeing in these "rtl-sdr" devices, and they tend to use higher-quality components. These DVB-T devices, for example, use a master clock that is good to about 100PPM--which for radios is rather seriously crappy. They won't have features like a DDC (usually FPGA resident) for fine-tuning the RX signal. The 8-bit resolution may be fine for some applications, but for others requiring higher dynamic range, that 8-bit resolution will be a killer. Plus many of the "high dollar" SDR devices offer TX chains as well as RX chains, and all the other comments apply for the TX chain as well.

    But one of the big things about "high dollar" SDR devices is that they're primarily designed as *development platforms* for developing SDR applications across a wide "spectrum" of fields of endeavour. So they include large FPGAs, those FPGAs allow you to perform part/all of your DSP algorithms at insane speeds inside the FPGA--speeds/sample-rates that would be impractical for a host-software implementation. Large/fast FPGAs are expensive, and that cost has to be passed on. Further, the "high dollar" SDRs typically offer bandwidths into/out-of the host at much higher sample rates than 3.2Msps. Yes, 3.2Msps, RX-only, 8-bit resolution, no-fancy features is entirely-adequate for a lot of different hobbyist work. But it's inadequate for a lot of other types of work for which the so-called "high dollar" SDRs are supremely-well suited.