We recently had a 16 year old student in our labs, and tried to teach him something about LTE, RF transmitters, spectrum analysis, and so on. Most of the stuff however was far too complex for him to understand, as many of the mathematical basics were missing. After talking to him for a day and doing weird measurements, it popped to my mind that I still have this DVB-T Stick and a Raspberry Pi at home, which might make a really cool project. So I brought both devices the next day and told the student to do some research on rtl-sdr.com and find a project he would like to do.
He wanted to track airplanes, as he found a flight tracking webserver could be easily implemented with the RTL-SDR stick and the Pi. What’s this flight tracking, anyhow? Airplanes are sending broadcast messages with information on their flight code, location, altitude, direction, speed, and many other information. The system is called ADS-B, Automatic Dependent Surveillance Broadcast, and the messages are modulated on a 1090 MHz carrier signal and sent once or twice every second.
We just need the RTL-SDR Stick, an 1GHz vertically polarized antenna, and some receiver software. So we went to the lab and were soldering a simple dipole antenna with a length of roughly 7.5cm. Other antenna examples can be found on the project webpageof rtl-sdr.com. Then we downloaded dump1090-mutability software, the compilation was easy with standard tools.
Plugging everything together, holding the antenna out of the window starting the software, and immediately we received some messages! We were of course immediately googling at the coordinates, to see where the airplanes were located and were heading to.
It took us a 1 hour effort to build an antenna and compile the software, and could receive some digital radio messages from far away. Pretty cool, isn’t it?