Running the programs

We are now ready to run the demodulator and the decoder. Before we do that, though, we need to connect the radio and the antenna.

Connect the antenna’s connector to the LNA. Next, connect the LNA to the RTL-SDR dongle. Finally, plug the dongle into your computer’s USB port.

Running the demodulator

The demodulator needs a few parameters so it knows how to set up the tuner. The demod-presets command makes this easier by providing presets for the known frequencies. If you run this command without any arguments, you will get a list of presets (among other things):

$ demod-presets
  /usr/local/bin/demod-presets PROFILE
  /usr/local/bin/demod-presets update


  PROFILE   name of the tuner profile
  update    fetch the latest profiles

supported profiles:

  americas  North and South Americas
  euraf     Europe, Africa, Middle East
  apac      Asia, Pacific

Pick a preset for your region and run demod-presets again. For example, let’s run it with euraf preset:

$ demod-presets euraf
Image of the demodulator running with euraf preset

Running the decoder

With the demodulator running, open up a new terminal window to start the decoder.

$ decoder

Output from the decoder will be logged in the terminal where you started it.

To run the decoder with paths different from the ones in this guide:

$ decoder -c /path/to/cache -o /path/to/downloads

Updating demodulator presets

The L-band presets used by demod-presets command may change from time to time. The program has an update feature which you can use to fetch the updated presets. To use this feature, run:

$ sudo demod-presets update

What next?

It will take a while for the files to arrive, so please be patient. You may also need to adjust the antenna so it’s pointed correctly. Antenna pointing is outside the scope of this guide, though. The best place to ask for help regarding this is our forum.

When successfully downloaded, files should appear in the output directory. If you used the values from this guide, that’s /srv/downloads.