Amplitude modulation with a square wave as the message signal

Dear all,

Hi,

I have written some codes which produce the output I want,as follow

{

clc;

clear all;

N = 1024; %N point FFT N>fc to avoid freq domain aliasing

fs = 4096; % sample frequency

t = (0:N-1)/fs;

fc = 280e6; %Carrier Frequency

fm = 100; %Three message signal frequencies

Ec = 20; %Carrier Amplitude

Em = 5;

A = Ec + Em*sin(2*pi*fm*t);

n=Ec*sin(2*pi*fc*t);

m=1+Em/2.*square(2*pi*fm*t)+(Em/2);

subplot(2,1,1);

plot(t,m);

xlabel('Time');

ylabel('Amplitude');

title('Message Signal');

grid on;

subplot(2,1,2);

plot(t,n);

xlabel('Time');

ylabel('Amplitude');

title('Carrier Signal');

grid on;

k=n.*m;

k( k<0 )=0;

Mf = 2/N*abs(fft(k,N));

f = fs * (0 : N/2) / N;

close all;

figure('Name','Time/Fequency domain representations of DSB-AM signals');

subplot(3,1,1); %Time domain plot

plot(t(1:N/2),k(1:N/2),t(1:N/2),k(1:N/2),'r',t(1:N/2),-k(1:N/2),'r');

title('Time Domain Representation');

xlabel('Time'); ylabel('Modulated signal');

subplot(3,1,2); %Time domain plot

plot(t(1:N/2),k(1:N/2),t(1:N/2),k(1:N/2),'r');

title('Time Domain Representation');

xlabel('Time'); ylabel('Modulated signal');

subplot(3,1,3); %Frequency Domain Plot

plot(f(1:256),Mf(1:256));

title('Frequency Domain Representation');

xlabel('Frequency (Hz)'); ylabel('Spectral Magnitude');

}

Now I want to replace 'm' signal with the following code,

{

t = 0:.1:20;

y = zeros(20,length(t));

x = zeros(size(t));

for k = 1:2:39

   x = x + sin(k*t)/k;

   y((k+1)/2,:) = x;

end

plot(t,y);

title('The building of a square wave')

}

But,cant squeeze it in correctly. I'm tired of looking at it now, would you please help me on that. I appreciate your help.

BW, S.

Answer 1

[S]

It's been done!