# Problem : Vector length is different and fail to show the result of spectrum frequency.

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ong jia eek on 1 Oct 2019
Below is my code for spectrum frequency
It seems that i couldn't display the spectrum frequency code and I have no Idea why
fc=input('Enter the carrier signal freq in hz,fc=');
fm=input('Enter the modulating signal freq in hz,fm =');
m=input('Modulation index,m= ');
tm=(1/fm)*2;
t=0:1/(fc*1000):tm;
c=cos(2*pi*fc*t);%carrier signal
M=sin(2*pi*fm*t);% modulating signal
subplot(3,1,1);plot(t,c);
ylabel('amplitude');xlabel('time index');title('Carrier signal');
subplot(3,1,2);plot(t,M);
ylabel('amplitude');xlabel('time index');title('Modulating signal');
y=cos(2*pi*fc*t-(m.*cos(2*pi*fm*t)));
subplot(3,1,3);plot(t,y);
ylabel('amplitude');xlabel('time index');title('Frequency Modulated signal');
F = 1000; % sampling frequency
f0 = fc; % carrier
f1 = fm; % modulating tone
beta = m; % modulation index
% signal, spectrum
N = 1000;
t = (0:N-1)*(1/F); % delt = 1us
z = fftshift(fft(y))/N;
f = (-N/2:N/2-1)*(F/N);
% predicted sidebands for the positive frequencies only
n = 4;
sidamp = (1/2)*besselj(0:n,beta);
sidamp = [fliplr(sidamp(2:end)), sidamp];
sidf = (f0-n*f1):f1:(f0+n*f1);
figure(2)
subplot(2, 1, 1);
plot(f,abs(z))
xlim([-2*f0 2*f0])
subplot(2, 1 ,2 );plot(f,abs(z),sidf,sidamp,'o')
xlim([f0-f1*10 f0+f1*10]) % sidebands at the pos frequencies

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