How to convert time domain to frequency domain

114 views (last 30 days)
This is my code, I failed to convert time domain to frequency domain, as I not sure on how to create the right frequency for frequency domain graph
%FM generation
clc;
clear all;
close all;
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= ');
t=(1/fc)*20;
t=0:0.0001:t;
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');
fs=1000;
z=fft(y);
subplot(2,1,4);plot(t,z);
figure;
ylabel('amplitude');xlabel('frequency domain');title('Frequency Modulated signal');
  1 Comment
Adam
Adam on 30 Sep 2019
You need to plot
abs(z)
or
abs(z).^2
if you prefer, rather than just z, which should be complex and will default to plotting the real part.

Sign in to comment.

Accepted Answer

Shubham Gupta
Shubham Gupta on 30 Sep 2019
Edited: Shubham Gupta on 30 Sep 2019
Replace the following line :
subplot(2,1,4);plot(t,z);
figure;
by the following code
nfft = length(y);
f = (0:1/nfft:1-1/nfft)*fs; % define frequency-domain
figure; % figure should be written before subplot to open new figure
subplot(2,1,1); % subplot(2,1,4) will give error beacause for a 2x1 vector valid indeces are 1&2, 4 is wrong
plot(f,z); % t (time-domain) is replace with f (frequency-domain)
Let me if you have any doubts
  2 Comments
Shubham Gupta
Shubham Gupta on 1 Oct 2019
I am glad it worked. In the above graph, every peak in y-axis shows that there is a signal of corresponding frequency shown in x-axis.

Sign in to comment.

More Answers (1)

Rumana Afrin
Rumana Afrin on 14 Jun 2022
Edited: Rumana Afrin on 14 Jun 2022
%Parameters
y1 = A_norm*sin(2*pi*100*t);
y2 = A_norm*sin(2*pi*200*t);
y3 = A_norm*sin(2*pi*300*t);
y4 = A_norm*sin(2*pi*400*t);
y5 = A_norm*sin(2*pi*500*t);
y6 = A_norm*sin(2*pi*600*t);
y = [y1; y2; y3; y4; y5; y6];
%Frequency content
X = fft(y);
fft_abs = abs(X);
figure;
for i = 1:6
A_norm(i) = A_norm(:,i);
X(i) = fft(y(i));
fft_abs(i) = abs(X(i));
subplot(3,3,i)
plot(fft_abs(i))
xlabel('Frequency(kHz)')
ylabel('Magnitude')
title('Frequency domain')
end
Hi, I do not understand where have I done wrong. Where A_norm is

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by