Slashdot Mirror

← Back to Stories (view on slashdot.org)

Getting Started With GNU Radio (hackaday.com)

Posted by timothy on from the good-gnews dept.

An anonymous reader writes: Software Defined Radio must be hard to create, right? Tools like GNU Radio and GNU Radio Companion make it much easier to build radios that can tune AM, FM, and even many digital modes. Of course, you need some kind of radio hardware, right? Not exactly. Hackaday has one of their video hands on tutorials about how to use GNU Radio with no extra hardware (or, optionally, a sound card that you probably already have). The catch? Well, you can't do real radio that way, but you can learn the basics and do audio DSP. The next installment promises to use some real SDR hardware and build an actual radio. But if you ever wanted to see if it was worth buying SDR hardware, this is a good way to see how you like working with GNU Radio before you spend any money.

11 of 42 comments (clear)

  1. SDR Hardware by PPH · · Score: 4, Insightful

    Entry level, about $12. I think I'll just go ahead and risk it.

    --
    Have gnu, will travel.
    1. Re:SDR Hardware by drinkypoo · · Score: 4, Interesting

      You piqued my curiosity so I plugged the part numbers for the ICs into eBay and got back the same thing for ten bucks shipped. If I were already doing a newegg order, though, I might well toss one in from them so as to get it this month.

      --
      "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
    2. Re:SDR Hardware by Tailhook · · Score: 4, Informative

      If you can add $10 to that rtl-sdr.com sell R820T/RTL2832U dongles (on Amazon) with temperature compensated oscillators, SMA connectors and other nice features for SDR experimentation. Start with that if you imagine using upconverters, front-end filters, etc.

      You'll want a short USB pigtail for these devices, though; they are fairly large.

      --
      Maw! Fire up the karma burner!
    3. Re:SDR Hardware by lkcl · · Score: 4, Interesting

      yeah i got something similar, i researched the chipset a bit in advance, to see what frequencies it could do. i found one that could go from i think it was... like... 100 mhz through to almost 1900mhz, with a bandwidth of something like... 2.8m-samples/sec. it only had an 8-bit ADC resolution but that was ok. i then used it with some software i was working with, at the time (passive GSM scanning software), and actually managed to find a couple of frequencies, which was amazing.

      going beyond that would have been tricky, because at the limit of 2.8 million samples per second of I and Q data @ 8 bit, it was pushing the limit of what the hardware could actually do: there were quite a few drop-outs. i'm sure the proprietary driver could handle that data rate, but the reverse-engineered gnu/linux one simply couldn't.

      anyway yes absolutely! $12 plus shipping for something that will handle a huge range of frequencies, FM radio, TV frequencies, GPS satellites, GSM 850 and 900mhz, and even some of the higher-end GSM frequencies @ 1800mhz... maan, what more could you ask for? :)

    4. Re:SDR Hardware by viking80 · · Score: 2

      Or you can stabilize the temperature of the crystal yourself. We used to build crystal ovens to stabilize crystal oscillators at a constant temperature, and heat it up to 40C (or 50C depending on where you live) with some resistors. Use a thermistor and a regulator to control the temp.

      Even without the oven, the R820 dongles on ebay from china gives you good stability after 10 minutes. You can listen to FM radio, Aircraft radio, old cellphones. I have one set up to receive aircraft tracking info as well as one for ship AIS. This gives me a nice map with view of all crafts in the area, with name, destination speed etc.

      --
      don't cut it off www.mgmbill.org
    5. Re:SDR Hardware by fuzzyf · · Score: 2

      It's worth mentioning that Michael Ossmann (creator of HackRF) is recording an online course about SDR and digital signal processing. It's ongoing, so there will be more videos as times go by.
      It mentions hackrf but you can do get by just fine with a regulrar cheap dongle.
      https://greatscottgadgets.com/...

      Thank you Michael Ossmann! :)

  2. Thanks a lot, 'progress'... by fuzzyfuzzyfungus · · Score: 2

    Back in the day, I could blame crippling hardware costs for my ignorance of signal processing. Now what am I going to do?

  3. Question: Evading Police radar-detector-detector? by mrops · · Score: 2

    Where I live, radar detectors are illegal.

    Naturally, police have Radar detector-detector built into their radars, and I know of one confirmed case where a friend visiting out of state got caught with his radar detector.

    So, can a radar detector built out of SDR/GNU Radio be detected? Hypothetically of coarse.

  4. probably, detects superheterodyne stage by raymorris · · Score: 2

    Yes, it probably will detect it, at least for inexpensive SDR hardware. Most modern receivers are the superheterodyne type, in which an oscillator within the receiver is set to a frequency near the frequency you wish to detect. This simplifies the circuitry and software because you're only processing the DIFFERENCE between the received signal and the reference, rather than directly processing the source waveform at some sample-rate multiple of the frequency of interest.

    The detector-detector picks up the oscillation of this reference frequency.

    A non-superheterodyne type could be used, but it would be significantly more expensive.

    Shielding MIGHT be an option, though one would have to be sure that the reference frequency doesn't leak out through the cabling and antenna, while allowing the input signal (at the same frequency) to come in.

    1. Re: probably, detects superheterodyne stage by gnu-sucks · · Score: 2

      Actually it can be done with a little RF theory.

      The way these things is by multiplying the incoming RF by a carrier of frequency very close to the radar frequency. The result is a lower-frequency product that can be sampled or simply compared in the analog domain to a reference. In this setup, the frequency we are multiplying by (the "LO" or "local oscillator") is what is detected remotely, because, as you point out, it has a very direct connection to the antenna.

      Here's how you get around it:

      Multiply by the expected radar frequency plus, say, 200 MHz. Before the multiplication, near the antenna jack, filter for radar frequency +/- 10 MHz (bandpass). Now the result of the multiplication will be very low-level signal except for a portion around f+/-10 MHz. You then sample this data. As you can see, the bandpass filter doesn't allow the LO to escape through the antenna connection.

      Traditional receivers wouldn't do this because it wastes a lot of potentially useful bandwidth, but you can do this to avoid having the LO detected. Without much background on speed radar, I don't know how much variance there is in radar guns, but you would need to take this into account when designing the input filter and choosing the offset from expected frequency for the LO.

      Not in textbooks, but definitely something that can be done.

  5. SDR transmitting by Rufty · · Score: 2

    For transmitting there's the HackRF which is a few mW output and is the one I've played with. Also another supplier that has cheaper, transmit only versions; the HackRF Blue
    For quite a bit more, there's MIMO capable devices such as the Ettus USRP that lets you run your own GSM basestation among other things.
    And for a more stand alone device, there's always the PortableSDR
    I've got a HackRF and am having fun with it trying to make a network analyzer. The others, I've just heard about.

    --
    Red to red, black to black. Switch it on, but stand well back.