Real time GPS decoding with software defined radio

In case the Realtek RTL2832u-based USB TV tuner dongle isn’t useful enough, the folks behind a project to get a software defined GPS receiver off the ground successfully plotted GPS data in real-time with this very inexpensive radio.

Previously, we’ve seen these dongles grab data from GPS satellites – useful if you’re building a GPS-based clock – but this build required hours of data collection to plot your location on a map.

The folks working on the GNSS-SDR project used an RTL2832 USB TV tuner and a Garmin active GPS antenna to track up to four GPS satellites in real-time and plot a location accurate to about 200 meters.

The Google Earth plot for this post shows the data collected by the GNSS-SDR team; the antenna was fixed at the red arrow for the entirety of the test, and the  yellow lines represent a change in the calculated location every 10 seconds. Amazing work, and only goes to show what this remarkable piece of hardware is capable of.

27 thoughts on “Real time GPS decoding with software defined radio

  1. I’m sorry, but this is just stupid. Why bother? It is too inaccurate for anything useful and it takes more time and effort than to just use a $50 android phone.

    Just lame.

    1. Why bother? Because you can. There are many things which started small and everyone asked why bother. Like combustion engine. This is one of the most relevant articles for this site, the very definition of a hack. If you don’t like it PLEASE don’t read this site.

      1. Everyone is entitled to their comments, go back to your cave if you DON’T like it Ready made GPS receivers are much cheaper and refined than a TV tuner, but the proof of concept is interesting..

    2. You’re right, why use your brain, learn, possibly create new things, have fun and experiment, when you can just buy something.

      Seriously, this is a great piece of work!

  2. The yellow line of your GPS system looks the same as mine.
    To go from one end to the other end of the same road, it takes me on the scenic route around town, going the wrong way along one way streets, ignores new roads and along footpaths too overgrown to walk down, never mind drive down.

  3. Maybe dumb or obvious question, but has anyone considered taking the better dongles out there and figuring out what they have in common, developing a superior open source version and publishing the schematics or kits? Whether this is more accurate than commercial GPS is secondary, the point is that with one device we can receive and process a wide range of signals from television to radio to gps, would be very nice to have one open source device made of better components that could do this. I find it very useful to have one device that can handle such a wide range of signals.

      1. There is the fact that they make them with bulk-bought parts, so it’s cheaper than what a dedicated OSI might get.

    1. These SDR hacks all rely on an unpublished mode available on certain commodity radio chips. I don’t know for sure, but those kinds of chips are often not available for purchase in small quantities and without signing an NDA. One reason, as with many more specialized ICs, is that the manufacturer doesn’t want to deal with small companies and individuals. Another possible reason is that the radio industry, and GPS in particular, is controlled by a rat’s nest of government regulations not the least of which are export controls on many things that could be used for building weapons. GPS, in particular, is regulated in that way because it would, in theory, be used to make ICBMs. SDR may, very well, fall under that same category because it can be used for GPS and much more.

  4. Don’t commercial GPS receivers shut themselves down if they travel too fast or too high? A homebrew GPS without these interlocks might be considered a weapon and attract some unwanted attention.

    1. Homebrew GPS devices have been made before and to the best of my knowledge nothing nasty has happened – all of the documentation needed for this is available. My guess is that they’ve taken the logical route – if anyone has the resources to build something nasty capable of traveling the required speed/height, GPS data decoding will be the least of their dificulties.

      1. Actually, as far as I’ve always heard, access to GPS telemetry (and high quality gyroscopes before the existence of GPS) IS one of the only components that most other countries lack in order to have accurate missiles. It’s the difference between the kind of missiles we launch vs. the incredibly inaccurate Scud missiles Iraq used to use.

        As for existing home-made GPS projects, the only one I remember seeing online was posted by a Russian man who, for obvious reasons, isn’t subject to US weapons export restrictions. Also, the law may look differently on individuals working on hobby projects vs. a company selling their product outside the U.S.

    2. True, but I’m pretty sure you can’t read the encrypted stream anyway, which limits it’s usefulness in that manner.

  5. ————————-
    Everybody above this line missed the point.

    GPS Modules have 2 limitations:
    1) Speed
    2) Altitude

    With a SDR, you don’t have any of those 2 limitations, PERIOD!

    1. Actually these restrictions only apply to ITAR compliant devices, i.e. those sold through the US. If you buy outside the US you can find GPS devices that don’t comply with ITAR restrictions and so keep working when they are travelling fast and/or high.

  6. I went gnss-sdr.org’s project page thinking that they might have created something balloon-able. Not with garden variety latex! But, it’s a nice proof of concept.

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