Amplitude modulation with a square wave as the message signal

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S
S 2015-3-18
回答： S 2015-3-19
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.

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S
S 2015-3-19
It's been done!

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