README.md

Pydemod

Pydemod is a set of Python 3 libraries and tools for demodulating radio signals. It does not intend to compete with full-featured packages such as GNU Radio. Instead, it strives to allow radio enthusiasts to gain hands-on experience with modulation schemes.

Pydemod relies on NumPy/SciPy.

On Ubuntu use

pipx install scipy --include-deps

Currently, the released modules include:

• physical layer:
  • phase demodulation (naïve)
  • Manchester decoding
  • basic logical levels (TTL-like) decoding and clock synchronization
• data link layer:
  • synchronization and error detection for polynomial codes
  • full implementation of RDS and AMSS codes
  • CRC calculation
• application layer:
  • functional AMSS decoder
  • functional temperature & humidity sensor decoder (supports protocols TX29 and Conrad) → see blog post (in French)
    • You can very easily receive signals using an RTL-SDR dongle, using a command like this: rtl_fm -M am -f 868.4M -s 160k - | ./decode_weather.py --protocol tx29 --squelch 4000 --rawle -

RDS bitstream decoding from wave file captured by the RTL-SDR dongle can be done using (file name and path is an example)

rtl_fm -f 104900k -s 228k -E wav /tmp/104900.wav

If your version of rtl_fm (check rtl_fm --help) does not understand the -E wav parameter, use sox to do it for you:

rtl_fm -f 104900k -s 228k -E wav - | sox -t raw -r 228k -es -b 16 - -c 1 /tmp/104900.wav

Then load your file and get the following output

./demodulate_rds.py --input "/tmp/104900.wav" --output "/tmp/104900.rds"
Sample rate: 228000 Hz, duration: x.xxx s

The 104900.rds bitstream file should then look like

cat /tmp/104900.rds 
1111001111111100000101110010010110111011010101011011000001010

This file you can load into redsea or RDSSpy.

Note that currently only 228k (= 4x 57 kHz) mpx files with an appropriate header can be used.

Pydemod is licensed under the terms of the GNU GPL v3.

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Pydemod is developed by Christophe Jacquet, F8FTK/HB9ITK.