Demodulation PSK31 in Python

This is a Python program to demodulate the psk31 known as QPSK modulation. This is the simplest example, and only the Terminal Unit part of the psk31 is implemented. See also https://en.wikipedia.org/wiki/PSK31

Source code

import wave
import math
import numpy as np

fname='psk31_sample8k.wav'  # should be specify the filename.
smp= 8000           # Sampling Rate
FQ= smp/1000.0      # Signal Frequency 
wind= 40            # window
waveFile = wave.open(fname, 'r')
q=[];i=[]
for j in range(waveFile.getnframes()):
      buf = waveFile.readframes(1)
      q.append((buf[0]-128)*np.sin(np.pi*2.0/FQ*j))
      i.append((buf[0]-128)*np.cos(np.pi*2.0/FQ*j))
      print(int(sum(q)>0),int(sum(i)>0),sep=",")
      if j>wind:q.pop(0);i.pop(0)
waveFile.close()

Sample sound file

should be convet to wave format. The input audio file should have a sampling rate of 8000 Hz and a quantization bit rate of unsigned 8 bits.

https://en.wikipedia.org/wiki/File:PSK31_sample.ogg

it is from wikipedia of psk31. If you decode it, it becomes "Welcome to Wikipedia, the free encyclopedia that anyone can edit."

Parameters

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

fname='psk31_sample8k.wav'  # should be specify the filename.
smp= 8000           # Sampling Rate
FQ= smp/1000.0      # Signal Frequency

fname
should be specify the filename.
smp
Sampling Rate.
FQ Signal Frequency. This sound example should be 1000.0.
This figure shows the spectral distribution of a sample sound file. There is a peak around 1000Hz.

Complex Plane and Value Assignment

Modify this line if you want to change the value assignment for the complex plane.

print(int(sum(q)>0),int(sum(i)>0),sep=",")

Usage

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

 python psk31.py > psk31_sample8k.csv