How do I assign frequency values to the obtained fft values without plotting . I need to know the value of the peak at 16Hz for further calculations.

clear all
close all
clc
L=10;
n=1.45;
c=2.9979e8;
dt = 6e-12;
T=10*2*L*n/c;

t = (-T/2/dt:1:T/2/dt)*dt;
Nt=round(T/dt);
fsine = 1e9;
vsine = 1;
phi = vsine*sin(2*pi*fsine*t);
EL1t=1.274e7*exp(1i*phi);
FP=fft(phi);
fs=1/dt/Nt;
Fs=(-1/dt/2:fs:1/dt/2-1);
Z=plot(Fs,fftshift(abs(fft(EL1t))));

I need to know the value at 16GHz in the plot.

Answer 1

[vidyesh]

Hi Yogesh,

You can use the max function to find the value of the peak and its index in the array.

Then use the index to get the corresponding frequency.

https://www.mathworks.com/help/matlab/ref/max.html

Add the below lines to your code.

pow = fftshift(abs(fft(EL1t)));
[val,ind] = max(pow)
f_max = Fs(ind);

Hope this helps

[Yogesh]

But the above command is for max value which is at 0GHz , but I want to know the value at 16GHz

[vidyesh]

I thought you wanted the value at peak (max value).

You can use the below code to find the value at a specific frequency:

freq_f = 16e9;
% nnz(Fs==freq_f) % returns 0

In this case it seems like array 'Fs' doesnt contain the exact value of 16 GHz, so we find the closest value.

[val,ind] = min(abs(Fs-freq_f)); % Find freq closest to 16 GHz
disp(Fs(ind));
disp(pow(ind));

[Yogesh]

Thank you Vidyesh , you were really helpful...