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Demodulation Radio Teletype (RTTY) in Python

This is a Python program to demodulate the radio teletype known as FSK modulation. This is the simplest example, and only the Terminal Unit part of the RTTY is implemented. The rest should be coded according to ITA2, for example.

Sample sound file

This ogg file should be converted to wave format. https://en.wikipedia.org/wiki/File:RTTY.ogg it is from wikipedia

Convert ogg file to wave format

Install ffmpeg and run:

ffmpeg -i RTTY.ogg -ar 8k -c:a pcm_u8 -f wav rtty3s.wav

Parameters

Some parameters in the source code need to be modified according to the audio file to be input.

fname='rtty3s.wav' # should be specify the filename.
smp= 8000          # Sampling Rate
FQm= smp/914.0     # Mark Frequency 914Hz
FQs= smp/1086.0    # Space Frequency 1086Hz
  • fname should be specify the filename.
  • smp Sampling Rate.
  • FQm smp / Mark Frequency
  • FQs smp / Space Frequency

How to specify the MARK & SPACE frequency

To find MARK & SPACE frequences, You can use any spectrum analyze tools on your PC. For example I use Sazanami Version 1.7.3 2020/10/22 .

  • MARK Frequency about 915Hz
  • SPACE Frequency is about 1085Hz

Usage

Please specify an appropriate audio file for the input. This program assumes 8KHz sampling, mono, 8bit quantization, and no sign.

python -m src.main

Demodulation example