I'm trying to complete one task: Download some FM modulated signals from page http://www.w1hkj.com/modes/index.htm. Calculate their spectrograms, i.e. short-time Fourier transform. Observe different FM patterns. Do some literature investigations. Try to recover bits that are coded by different frequency values (states).
At first I displayed a spectrogram:
clc; clear; close all; [y,fs] = audioread('Olivia16-500.wav'); spectrogram(y, 512,256,512, fs, 'yaxis');
And the other part is: Try to recover bits that are coded by different frequency values (states). I guess I should demodulate signal, so I did the following:
Nx = length(y); n= 0:Nx-1; dt = 1/fs; t = dt*n; fc=200; figure(1) z=demod(y,fc,fs,'fm'); plot(t,y, 'c', t,z, 'b'); xlabel('Time'); ylabel('Amplitude'); legend('Modulated signal', 'Recovered signal');
And the output:
Did I understand the task correctly or did I miss something? Thank you for any advices.