Question

Message Carler cos (20.000rt) modulation index: 0,2 signal: 2 cos (2001tt) signal : - Modulate and demodulate these 2 signals and plot time domain and frequency spectrum for all steps Write whole code clearly. Use Matlab.

I need Matlab code

Answer 1

MATLAB:

fc=10000%career frequency

fc = 10000

fs=10*fc;%sampling freqeuncy

N=2000;Ts=1/fs;

t=[0:Ts:(N*Ts)-Ts];

mt= 2*cos(200*pi*t);

m=0.2;%Modulation inde

Ac=2/m;

ct=Ac*cos(20000*pi*t);

AM=mt.*ct;

figure;

subplot(221)

plot(t,AM,'g');title('AM signal');xlabel('t');ylabel('amplitude ');grid on

%Frequency spectrum

f=[-fs/2:fs/N:fs/2-fs/N];

subplot(222)

stem(f,fftshift(abs(fft(AM))),'r') ;

xlabel('f in Hz');ylabel('Magnitude');grid on;

title('Amplitude spectrum of AM signal');xlim([-2*fc ,2*fc])

%Demodulation

y1 = AM.*ct/Ac;

[b a] = butter(11,fc*2/fs);

y = filter(b,a,y1)/5;

subplot(223)

plot(t,y,'m'); title('Demodulated signal')

grid;xlabel('t')

ylabel('amplitude ')

AM signal 20 Amplitude spectrum of AM signal 10006 8000 10 6000 amplitude Magnitude 4000 - 10 2000 -20 0.01 0.02 t Demodulated signal 0 fin Hz 2. *10* N amplitude -1 -2 0.02 0.01 t