Frequency Modulation

clear all;
close all;

tin=0.15;
Fs=2000;

t1=0:1/Fs:tin/3;
t2=tin/3:1/Fs:2*tin/3;
t3=2*tin/3:1/Fs:tin;

len1=length(t1);
len2=length(t2);
len3=length(t3);

for i=1:len1
   
  me1(i)=1; 
  me2(i)=-2;
  me3(i)=0;
   
   
end

me=[me1 me2 me3];

t=[t1 t2 t3];

f=linspace(-Fs/2,Fs/2,length(me));

fc=200;

carrie=cos(2*pi*fc*t);

kf=50;%deviation constant






integme=integro(me);

modulate=cos(2*pi*fc*t+(2*pi*kf*integme));


figure(2);
plot(t,integme);
title('Integral of Message Signal');
figure(3);
subplot(211);
plot(t,me);
title('Message Signal');
subplot(212);
plot(t,modulate);
title('fm modulation signal');

ffme=fftshift(fft(me,length(me)))/length(me);

ffmodulate=fftshift(fft(modulate,length(me)))/length(me);

figure(15);
plot(f,abs(ffme));
hold on;
plot(f,abs(ffmodulate));
legend('message','modulated');




function reslt=integro(x)
Fs=2000;
dt=1/Fs;
result1=0;
for i=1:length(x);
   
    result1=result1+(x(i)*dt);
   result(i)=result1;
end

reslt=result;


end