Clear Filters
Clear Filters

Why do I see no Carrier Modulation Component?

1 view (last 30 days)
Ted Baker
Ted Baker on 31 Mar 2020
Edited: Ted Baker on 31 Mar 2020
Hi, I'm trying to simulate some amplitude modulation using an example from "The Art of Electronics (Horowitz)". the author says a data signal may be amplitude modulated with a carrier by the following:
Which by expanding the product results in three terms - the carrier and the two sidebands. I created the following matlab to test this:
close all;
Ac=1;
Am=1;
fc=100;
fm=10;% fm<fc
m=0.5;
t=0.2;
t1=linspace(0,t,1000);
y1=cos(2*pi*fm*t1); % message signal
y2=cos(2*pi*fc*t1); % carrier signal
eq=(1+m.*y1).*y2;
heq = hilbert(eq);
ffteq = fft(eq);
n = length(eq);
f = (0:n-1)*(100/n);
power = abs(ffteq).^2/n;
figure(1);
hold on
plot(t1,eq);
plot(t1,-abs(heq),'r-', t1,abs(heq),'-r')
xlabel('Time');
ylabel('Amplitude');
title('Modulated signal');
hold off
figure(2);
plot(f, power)
But my fft shows only the sidebands - no carrier at all - supressed carrier modulation. How should I alter my script to show the carrier in the fft? I see MatLab has ammod function, but I cannot get that to work at all. :/ Thanks in advance.

Answers (0)

Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!