PRACTICAL MATLAB® FOR ENGINEERS PRACTICAL MATLAB

Time Domain Representation of Continuous and Discrete Signals 87

MATLAB Solution

% Script file: modulation

figure(1)

subplot(2,2,1); % analog signals

fplot(‘3*cos(5*t)’,[0 3 -6 6]);

title(‘Information signal: 3*cos(5*t)’);

ylabel(‘Amplitude’);xlabel(‘time’);

subplot(2,2,2)

fplot(‘cos(50*t)’,[0 0.5 -1.5 1.5]);

title(‘Carrier signal: cos(50*t)’);

ylabel(‘Amplitude’);xlabel(‘time’);

subplot(2,2,3)

fplot(‘3*cos(50*t)*cos(5*t)’,[0 3 -6 6]);

title(‘AM (Amplitude Modulated) signal’);

ylabel(‘Amplitude’);

xlabel(‘time’);

subplot(2,2,4)

fplot(‘3*cos((50*t)+3*cos(5*t))’,[0 2 -6 6]);

title(‘Angle Modulated signal’);

xlabel(‘time’);

ylabel(‘Amplitude’);

figure(2)

a=3*ones(1,50);

b=ones(1,50);

clock = [a b a b]; % discrete/binary signals

t = linspace(0,4,200);

carrier = cos(50*t);

subplot(2,2,1)

plot(t,clock);title(‘Binary information signal’);

axis([0 4 0 4]);ylabel(‘Amplitude’);

xlabel(‘time’);

subplot(2,2,2)

ASK= carrier.*clock;plot(t,ASK);

title(‘ASK signal’)

axis([0 4 -4 4]);ylabel(‘Amplitude’);

xlabel(‘time’);

subplot(2,2,3)

FSK=cos(20*t.*clock);

plot(t,FSK);xlabel(‘time’)

axis([0 4 -1.3 1.3]);ylabel(‘Amplitude’)

title(‘FSK signal’)

subplot(2,2,4)

PSK=cos(50*t+clock);

plot(t,PSK);

title(‘PSK signal’)

xlabel(‘time’); ylabel(‘Amplitude’);

axis([0 1.5 -1.3 1.3]);

Back in the command window the script fi le modulation is executed and the results are

shown in Figures 1.73 and 1.74.