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.

Comments

  1. presjar says:

    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.

  2. sonofabit says:

    i’m not sure if it’s just me, but http://www.gnss-sdr.org/ is out of order :(

  3. RicoElectrico says:

    Why not throw out low-accuracy crystal and install a (V)TCXO?

  4. Danny says:

    Yer its down, but this is up :)

    http://sdr.osmocom.org/trac/wiki/rtl-sdr

  5. Mark A says:

    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.

  6. OpenSource says:

    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.

  7. kevin says:

    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.

    • daqq says:

      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.

      • Colecoman1982 says:

        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.

    • draeath says:

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

  8. Jörgen Van says:

    ————————-
    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!

    • malvineous says:

      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.

  9. cmholm says:

    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.

  10. Doktor Jeep says:

    Out-standing!

  11. If someone is interested in the details, there is a paper about this hack available at http://www.cttc.es/publication/turning-a-television-into-a-gnss-receiver/

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