fs=100000; %sampling frequency
ts = 1/fs ; % time interval between sample point
t = 0 : ts :0.02; % scale of time, maximun=0.02
N= size(t,2);
fm=100;
Vm=2*sin(2*pi*100*t);
fc=10000;
Vc=10*cos(2*pi*10000*t);
Vfm= 10*cos(2*pi*fc*t + 2*sin(2*pi*fm*t)); %modulated signal= Vfm
subplot(4,1,1);
plot(t,Vc);
ylabel('Amplitude (V)');
xlabel('Time(s)');
title('Carrier Signal Time Domain Representation');
grid on;
subplot(4,1,2);
plot(t,Vm);
ylabel('Amplitube (V)');
xlabel('Time (s)');
title('Message signal Time Domain Representation');
grid on;
subplot(4,1,3);
plot(t,Vfm);
ylabel('Amplitube (V)');
xlabel('Time (s)');
title('Frequency Modulated Signal Time Domain Representation');
grid on;
f=fs*(0:N/2)/N;
Vfm_f = (2/N)*abs(fft(Vfm,N));
Vfm_f=Vfm_f(1:floor(N/2)+1); % take the half: positive frequency
subplot(4,1,4);
plot(f,Vfm_f);
xlim([5000 15000])
ylabel('Amplitube (V)');
xlabel('Frequency(Hz)');
title('Frequency Modulated Signal Frequency Representation');
grid on;
