Modern planes use ADS-B or automatic dependent surveillance - broadcast to broadcast their callsign, current position, speed and flight direction. Being a safety critical system in a very diverse environment the messages are transmitted as plain text. As such anybody listening on the correct frequency and with the correct tools can read these messages.

One simple approach for this is ModeSDeco2. It can be used with simple RTL-SDR dongles and shows tracked planes in a webinterface with and underlying map from Google Maps.


Map View

ModeSDeco2, Map View

Flight List

ModeSDeco2, Flight List

Message Stats

ModeSDeco2, Message Stats

Setup & Running

  • Download ModeSDeco2 from here
  • Unpack the archive
  • Insert RTL-SDR dongle

The following command can be used to start with very basic configuration

./modesdeco2 --gain 49.6 --freq-correction 62 --web 8088 --beast 10003 --msg 30003 --sbs10001 10001 --device-serial 00000001

ModeSDeco2 will then listen on


As always using a proper antenna will significantly increase the reception quality. A very simple antenna design which works nicely for ADS-B is a groundplane antenna. The antennas can simply be made from 5 pieces of wire and a BNC or N-type socket. The length of the wires can be calculated with one of the many groundplane-antenna calculators out there.

The antenna depicted below is made of 1,5mm² solid copper wire. Each piece of wire is 65mm long. I started of with longer pieces of wire and cut them down after having them connected to the socket.

Groundplane Antenna


Also thanks to Johannes Weber for the idea!