Frequency Modulation for B>0.4

Hello!

My teacher asked me to modulate a signal with a Beta over 0.4, and asked me to use a formula, but I can t find it anywhere.

I am not allowed to use matlab FM function.

This is the formula for Beta<0.4:y=amply*cos(2*pi*Fc*t+B*sin(2*pi*Fm*t)).

Where y=modulated signal; Fc=carrier frequency, Fm=modulator frequency

Answer 1

[V Sairam Reddy]

Hi Stefan,

I understand that you are trying to implement frequency modulation for beta>0.4 without using the MATLAB in-built function.

Please find the formula and implementation of the frequency modulation :

% Matlab in-built function for Frequency Modulation
% y = fmmod(x,fc,fm,fDev);

% Equation for Frequency Modulation :
% y = A*cos(2*pi*Fc*t + 2*pi*Kf*integral(m(t)dt from 0 to t)) where m(t) is
% the message/input signal.

% Integral of input signal is summation of that signal which is equivalent to cumsum(x)/Fs
integral_x = cumsum(x)/Fs;
y = 1*cos(2*pi*Fc*t + 2*pi*freqdev*integral_x + initial_phase); 

To know more about the in-built functions that are implemented in MATLAB, select that function in your code, right click and select "open 'function_name'" as shown :

Please refer to 'fmmod' documentation to know more about frequency modulation in MATLAB.