This weekend I’ve learned that it is possible to catch some FT8 traffic using a simple RTL-SDR and a random telescopic antenna (like the ones on the old radios). No need for any filters, amplifiers or upconverters.
Software used
- GQRX - to receive and demodulate the signals from the SDR
- WSJT-X - to decode the audio received from gqrx to a human readable text
- GridTracker2 - to visualize the data from wsjt-x to on a map.
How?
- Check the “No limits” option in GQRX so that it allows you to tune outside of the supported range
- Choose the USB modulation
- Tune to the 7.074 Mhz.
- Pipe the audio from GQRX to WSJT-X. I’ve used pipewire with pavucontrol
- Enable the UDP server in WSJT-X settings. The GridTracker should pick it up immediately.
What is FT8?
FT8 is a digital mode used by the radio amateurs to exchange the bare minimum amount of information needed make a contact. Call sign, location, signal strength. There is a similar piece of software that can also attach short text messages - JS8Call
What is the point?
The FT8, WSPR and similar protocols are mainly used to check the current signal propagation in the earth’s atmosphere at any given moment for any given frequency band. However, it’s a pretty good demonstration of how one can relatively easily contact people thousands of kilometers away using just few watts of power.