Receiving ADS-B on the SDR dongle

I hadn’t anticipated moving up into the GHz range with this cheap little gadget yet but as it turns out, receiving and decoding the pulse trains that make up ADS-B is even simpler than using it to explore VHF/UHF.

This is entirely due to the excellent software available for this purpose.

These dongles are not plug-n-play and there are numerous ways to configure them – all this added to initial confusion in my case as a lot of disparate software had to be downloaded to make everything work. After that learning curve, ADS-B was simple.

ADS-B is far more common among European hobbyists than it is with us here in the States due mainly to the fact that is has been in use there longer. In a nutshell, ADS-B (Automatic Dependent Surveillance – Broadcast) is the name given to the system by which commercial (and some private) aircraft transmit their GPS coordinates to each other and to air traffic controllers on 978 MHz and 1090 MHz. This allows them to be seen, plotted and directed by ATC independently of radar.

This means that air traffic control can have highly accurate aircraft positions in places where radar wouldn’t be feasible – here in Houston, that initially meant helo flights to the Gulf of Mexico to and from off-shore oil rigs, but now it’s gone mainstream.

These latest SDR dongles are the first to have the speed and resolution to be able to decode ADS-B pulses. These pulses contain an aircraft’s GPS position, ID, altitude and speed with this info being transmitted once per second. Every 5th transmission from an aircraft contains additional data (tail number, squawk code, etc).

With the aircraft’s position being GPS-derived and updated every second, ADS-B is more accurate than radar (especially at long distances) and is updated more often. A typical air traffic control radar’s antenna takes 12 seconds to make one revolution – that’s 5 updates per minute versus 60 for ADS-B.

Enough about what ADS-B is – here it is as received on an $18 receiver and processed/displayed with free software:

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Plane Plotter displays the packet data either textually, as shown her, or on a map. The packets themselves are decoded by SDR# (read: SDR sharp) that runs in the background.

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This is still Plane Plotter – normally a map would be displayed and the aircraft’s position would be overlayed onto it. There are numerous detailed maps for many European areas and airports but I don’t have one for my area. But on to the next pic:

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Plane Plotter allows the user to overlay aircraft onto a Google Earth map. Here is Houston Intercontinental Airport with the three jets’ position plotted based on their ADS-B transmissions as received by me. I was about 4 miles away. One United jet can be seen taxiing south from the northermost runway, another United jet is taking off and the third jet has just landed. These planes are shown in motion by Plane Plotter, updated every second.

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Zooming out in Google Earth shows planes arriving and departing from the airport. I was able to receive ADS-B transmissions from planes 40 miles away with the generic antenna indoors in an office building.

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  2 comments for “Receiving ADS-B on the SDR dongle

  1. N7UN/Guy
    February 21, 2013 at 2:20 pm

    Really cool John! One advantage is ADS-B provides 3-axis info; altitude in addition to lat/longs which is independant of the aircraft altitude encoder. And most importantly aircraft info can be received by other nearby aircraft, providing cockpit “situational awareness” that was never available before to a flight crew.

    Interesting UPS Airlines was instrumental in the development and initial testing….back in the late ’90s!

    What’s your best aircraft DX?

    73, Guy/N7UN

    • February 21, 2013 at 3:16 pm

      It is an amazing use of technology. For $20 and a computer, anyone can now have a virtual radar display of the air traffic around them. I don’t know what practical use that serves but it is cool to see planes miles away heading in your direction – and then see it overhead as it gets nearer.

      My best DX is 40 miles – others report a bigger radius when using a dedicated antenna for 1090 MHz.

      The weak link in ADS-B is that the plane’s transponder needs to be on and operational. Which is why primary radar will still be necessary & valid – an important consideration for me ;-)

      My next use of this gadget will be an attempt to receive NOAA wx sats on 138 MHz…check out this blog
      http://st2nh-blogger.blogspot.com/

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