Two Software Defined Radio Hacks From Our Resident SDR Guru

It seem [Balint] is becoming somewhat of a SDR guru around these parts; in the past few months, he’s gotten a USB TV tuner receiver working with GNU Radio, started a software defined radio tutorial YouTube channel, and even used this project to listen in on conversations between airplanes and air traffic control. This time, [Balint] is back using this cheap USB TV tuner for radio direction finding and running HDSDR in Linux and OS X.

[Balint]’s radio direction finding presentation goes over traditional means of direction finding using the doppler effect and mechanically rotated antennas. Because [Balint] is dealing with frequencies around 150MHz (about 2 meter wavelength), building a physical direction finding setup requires spinning antennas at around 40,000 RPM; much to fast for any hardware build. [Balint]’s solution was to attach 4 antennas around the circumference of a circle and electronically switch between them many thousands of times a second. [Balint] put up a wiki page going over all the theory and implementation details of his build.

[Balint] also put wrote up a neat app to control software defined radios – including the Realtek TV dongle –  over a network. Spread over a wide enough geographic area, it could become extremely easy for anyone to play air traffic controller. The BorIP Server can also be used to run HDSDR in Linux and OS X under Wine; just connect HDSDR to the network loopback on the same machine, and you get around Wine’s distaste for accessing hardware natively.

Awesome work, and we can’t wait to see what comes out of [Balint]’s laboratory next.

Edit: instead of the dongle, [Balnt] is using a ‘real’ software radio board. A lot of people are messaging him asking if the same method of direction finding is possible with the dongle. Here’s what [Balint] has to say:

The trick, as I see it, would be to create some (more or less simple) additional hardware to take the clock signal straight off the dongle’s on-board oscillator and divide it down for use with the antenna switch, i.e. 28 MHz à tens of kHz (this is the bit that’s done in ‘software’ on the FPGA). One problem still remains however: the counter needs to remain calibrated against the known direction the antenna was pointing at the time – otherwise a stop/start of the data stream from the dongle will mean the direction will go out of sync by 90/180/270 degrees each stop/start. Perhaps someone will figure out an elegant solution for this slight hurdle!

So there you go. Up for a challenge?

13 thoughts on “Two Software Defined Radio Hacks From Our Resident SDR Guru

  1. “This time, [Balint] is back using this cheap USB TV tuner for radio direction finding”

    What a nonsense, Brian Benchoff. You really should spend a minute or two to do your research before posting.

  2. > What a nonsense

    I believe you meant to say “What nonsense.”

    Don’t you just hate it when pedants latch on to the tiniest error to completely disregard everything you say?

    1. In Britain you wouldn’t be a pedant — you’d simply be wrong.

      English is spoken outside of your cherished 50-mile radius, no matter how silly it may sound to your ‘Merican ears.

    1. You use the doppler effect to look at the phase change of the frequency rather than just the amplitude of the signal at a certain direction. Looking at only the amplitude trying to figure out where a signal is is terribly unreliable because of the nature of RF waves. Im not an expert but drove around today with a directional YAGI antenna looking for one of my friends and I can tell you its just a pain. haha

      1. That’s because you’re supposed to use an antenna with a strong null, like a loop antenna. Then, you search for the SILENCE – works much better, because you are much less likely to be fooled by reflections.

  3. he’s gotten a USB TV tuner receiver working with GNU Radio

    Huh … Antti Palosaari is the one who found the possibility of doing this for the RTL sticks and Steve Markgraf is the one who did the first software to get the sample live and allowed usage with GNURadio. Balint made more convenient to use. And his code is now quite obsoleted by the latest osmocom rtl-sdr gnuradio block.

  4. Why on Earth would you need to switch antennas in your Doppler array at such a high frequency? T-Hunters around the world have been switching antenna arrays at +/- 500 Hertz for decades with most excellent results…

    Responding in part to draeath, loop antennas with a good, sharp null are very useful when T-Hunting in the HF bands or low VHF due to size constraints, but for VHF and UHF I’d much rather have a lightweight Yagi antenna and attenuator. I’ve put the same yagi that I use on foot on the end of an extendable paint pole and stuck that out the vehicle window for mobile hunts. (Google Tape Measure Beam for an interesting article on a much-used design, great for on-foot hunts in heavy brush.)

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