Fox Hunting With Software-Defined Radio

Fox hunting, or direction finding, is a favorite pastime in the ham radio community where radio operators attempt to triangulate the position of a radio transmission. While it may have required a large amount of expensive equipment in the past, like most ham radio operations the advent of software-defined radio (SDR) has helped revolutionize this aspect of the hobby as well. [Aaron] shows us how to make use of SDR for direction finding using his custom SDR-based Linux distribution called DragonOS.

We have mentioned DragonOS before, but every iteration seems to add new features. This time it includes implementation of a software package called DF-Aggregator. The software (from [ckoval7]), along with the rest of DragonOS, is loaded onto a set of (typically at least three) networked Raspberry Pis. The networked computers can communicate information about the radio waves they receive, and make direction finding another capable feature found in this distribution.

[Aaron] has a few videos showing the process of setting this up and using it, and all of the software is available for attempting something like this on your own. While the future of ham radio as a hobby does remain in doubt, projects like this which bring classic ham activities to the SDR realm really go a long way to reviving it.

7 thoughts on “Fox Hunting With Software-Defined Radio

  1. Yes, some hams get intrigued by building really small transmitters to be found , and a few are interested in building new things to do direction finding.

    But I suspect it’s mostly non-technical types who spend the most time at it. They don’t call it “radiosport” for nothing.

    The more that thehobby is promoted as an end, the less appealing it is to technical types.

    And I don’t see how SDRs has “revolutionized” direction finding. There’s lots of existing equipment, even I have an Icom walkie talkie. And those Bao-Feng walkie talkies are cheap, and as receivers are fine. So if SDR is cheap, it’s probably less an improvement here. So many SDR stories here are really about “it’s cheap and everywhere and you don’t have to build anything”.

    This seems to network receivers, but it’s not the SDR that does that.

    1. They have revolutionized the radio hobby in another way: From what I’ve read, many, perhaps even most, new ham radio models are based on SDRs, especially the cheap ones like Baofeng and the like.
      Most of these radios bear little to no resemblance to the SDRs we’re familiar with seeing on this site, instead they are made to look more like bog standard ham radios, even though a computer-like interface could be far more useful for many things.
      Just my 0.02 dollars. :D

      1. You have to think the SDR revolution started a lot farther back than most people think. I was working with synthesized transmitters and receivers a long time before we had radios on silicon fully controlled by processors. I see that as the advent of this revolution. Back then, we controlled the radios with shift registers or switches. It didn’t take much to move to cpu control, and my first efforts there used Visual Basic (it’s rare I admit to programming in VB) and the Centronics parallel printer port. Serial output and outboard serial-to-parallel converters followed. I wasn’t the game changer, but I was in front of the pack. Shortly afterward, or maybe before, ham manufacturers started using synthesizers, commercial vendors took them farther. SDRs were a natural outgrowth.

        Right now I have at least 6 SDR dongles around the shack, as well as a fully synthesized adaptive Micom3F and a Barrett 4050 SDR doing various things. The Kenwood TS480 rounds out the mix as the iconic synthesize, non-SDR radio. My ionospheric and lightning all depend on SDR and serious computational capabilities.

        The digitally controlled radio has revolutionized the hobby, IMNSHO even though it means many fewer people actually build their own complete hardware complement.

    2. Thinking similar where like; auto gain control issues with analog devices, the SDR’s are even worse unless easier to control.

      There are the classical mechanical ways to basically mini Faraday Cage the receiver with or without an antenna and use harmonics of the fundamental transmitter signal to narrow down location once in closer proximity if you can’t easily control the AGC.

      Still, if dealing with a computer interface or decent more basic screen real-estate, would be awesome to see more older smaller pieces of analog equipment hacked to interface with the newer bus communications protocols so that the SDR and DSP software applications or other code can process the older analog equipment signal path that might have significant improvements in performance. Not always, though thinking that way at least from this perspective on the situation and comment left blank.

      When I last left off on the CE-232 I realized all the work I did on the PCB etch resist wasn’t scaled correct. That left me thinking… OK… why am I even using that old design and not upgrading to a more modern interface and design. I can design a new board even with the same components used. That, along with hacking out the TDS’s to use for signals work and RDF, was one of those moments that sparked my learning curve to where I’m at now. With an SDR as an adapter or discriminator or not for further signals processing.

      Maybe this comment will help inspire more Bill Cheek moments to advance the older pieces of equipment in not only classic ways.

      Any ideas out there?

    1. The receivers could easily be carried by a drone, but the challenge is the antenna aperture size to spread out for electrical distance between the receivers. Doing this across multiple drones is harder since you need time sync between drones or time drift will cause errors in the answer.

  2. Fox Hunting still goes strong in the Balkans.( Romania, Serbia, Hungary Albania, Bulgaria …). I quit about 10 years ago, but my friends still hold contests every year. In the not so distant past, the best receivers were the Soviet ones, while new ones with features like a sound compass begin to appear and take over.
    Miss those days

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