What is the difference between demod and ammod?

I want to modulate a massage signal then demodulate that signal.

When i use demod then the demodulated signal is different than actual signal , but when i use ammod it works perfectly. what is the difference between those two?

My full code:

    % clear all the work space
    clc;clear all;close all;
    
    % Get user input
    % h = input("Enter the modulation index:"); % 1
    % Am = input("Enter the massage amplitude:"); % 10
    % Fm = input("Enter the massage frequency:"); % 200
    h = 1;
    Am = 10;
    Fm = 200;
    % Set Carrier frequency and amplitude based on modulation index
    Ac = Am/h;
    Fc = Fm*10;
    
    % Define time
    t = linspace(0,0.2,100000);
    
    % Generate massage signal
    ym = Am * cos(2*pi*t*Fm);
    figure("Name","Problem");
    subplot(5,1,1);
    plot(t(1:10000),ym(1:10000));
    grid on;
    title("Massage Signal");
    
    
    % Generate Carrier Signal
    yc = Ac * cos(2*pi*Fc*t);
    subplot(5,1,2);
    plot(t(1:10000),yc(1:10000));
    title("Carrier Signal");
    
    
    % Generate Modulated Signal
    y = modulate(ym,Fc,100000,"am");
    subplot(5,1,3);
    plot(t(1:10000),y(1:10000));
    title("Modulated Signal");
    
    
    % Demodulation Signal
    yd1 = demod(y,Fc,100000);
    yd = amdemod(y,Fc,100000);
    subplot(5,1,4);
    plot(t(1:10000),yd(1:10000));
    title("Demodulated Signal(Ammod)");
    ylim([-10 10]);
    
    subplot(5,1,5);
    plot(t(1:10000),yd1(1:10000));
    title("Demodulated Signal(Modulate)")

Answer 1

[Kunal Kandhari]

Hi,

demod(y,fc,fs,method) demodulates the real carrier signal y with a carrier frequency fc and sample rate fs using the method specified in method. By default it is: am i.e., Amplitude demodulation

Whereas amdemod(y,Fc,Fs) returns a demodulated signal z, given the input amplitude modulated (AM) signal y, where the carrier signal has frequency Fc. The carrier signal and y have sampling frequency Fs. The modulated signal y has zero initial phase and zero carrier amplitude, resulting from a suppressed-carrier modulation.

You can read more about both of this functions from the following documentation:

• demod documentation
• amdemod documentation