fmod.m

PLL in Matlab for FM Demodulation

function [outfm, phase] = fmod(msg, fc, fs, Ac, kf, flag)
%  FMOD()   -  This function performs frequency modulation, FM. The       %
%              integration of the message signal is perform here.         %
%                                                                         %
%                                                   t                     %
%        Equation:   s(t) = Ac*cos(wc*t + 2pi*kf * SUM m(t) )             %
%                                                   0                     %
%  msg - message signal vector (see note                                  %
%  fc  - carrier frequency                                                %
%  fs  - sampling rate for digitizing                                     %
%  Ac  - amplitude of carrier                                             %
%  kf  - modulation index                                                 %
%                                                                         %
%  Note:  If the message is sampled at a lower frequency, say 8 kHz, it   %
%         must be interpolated to the sampling rate supplied here before  %
%         calling this function.                                          %
%-------------------------------------------------------------------------%

%*************************************************************************%
% Filename  FMOD.M                                                        %
%                                                                         %
                                                    %
%*************************************************************************%

t = 0:1/fs:(length(msg)-1)/fs;                 % number of samples        %
phase = 0;
ph_count= 0;

if (flag == 0)
	for x = 0 : 1/fs : (length(msg)-1)/fs
		ph_count= ph_count+ 1;
		%if mod(x, 1000000/fs) == 0
		if mod(x, (0.25*length(msg))/fs ) == 0
			phase(ph_count) = (rand()*2*pi);
			%phase = phase + (2*pi/4);
			%if phase > (2*pi)
			%	phase = phase - (2*pi);
			%end
		else
			phase(ph_count) = phase(ph_count-1);
		end
	
	end
end	

%figure
%plot(t,phase);
%pause

if(nargin < 5)
   kf = (fc/fs) * (2*pi)/(max(max(abs(msg))));          %modulation index %
end;

outfm = Ac * sin( 2*pi*fc*t + 2*pi*kf * cumsum(msg) + phase);	%Generates FM modulated signal

end