How can I plot a message signal?

I want to plot the message m(t) signal from a AM signal. The carrier frequency is fc=522Hz. How can I code this so that the plot is the message signal?

Answer 1

[Rahul]

Hi Dimitrios,

Assuming a general Sideband-Suppressed modulation case, we can take a case of modulating a simple sine wave message signal of frequency fm (say 0.2*fc < fc) and an amplitude of 5, along with a sampling rate fs (> 2*fc : Nyquist Condition), we can plot each of the message, modulated and demodulated signals using the following snippet:

% Carrier Frequency
fc = 522;
% Sampling Frequency (> 2*fc)
fs = 100*fc;
% Message Signal Frequency
fm = 0.2*fc;

% Time Frame : 0 to 0.01 (s)
t = (0:(1/fs):0.02);

% Original Message Signal m(t) 
m = 5*sin(2*pi*fm*t); 

% Amplitude Modulated Signal
y_am = ammod(m, fc, fs);

% Amplitude Demodulated Signal
y_m = amdemod(y_am, fc, fs);

% Plotting each signal
plot(t, m)
hold on
plot(t, y_am)
plot(t, y_m, "o-")
hold off
legend(["Original Signal" "Amplitude Modulated Signal" "Demodulated Signal"]);

You can refer to the ammod (AM Modulation) and amdemod (AM Demodulation) MATLAB functions documentation for further customizing the code as per your needs.

[Dimitrios Kyriakidis]

Thank you very much