Plotting FFT Spectrum using Square Wave

I am trying to plot an FFT spectrum but the graph stops at half of the window I'm looking to acquire.

This is the code that I have used:

% clc;

% clear all;

t = 0:(1/1e6):(10/1e5);

x = 2.5*square(t*2*pi*1e5,50);

N = length(x);

fs = 10e5;

figure(1)

plot(t,x)

X = abs(fft(x));

bins = (0:(N-1));

f = (bins*fs)/N;

intN = ceil(N/2);

figure(2)

plot(f(1:intN),X(1:intN))

xlabel('Frequency (Hz)')

ylabel('Amplitude');

title('FFT Spectrum of Square Wave with 100kHz Frequency and 50% Duty Cycle');

xlim([0 1e6])

set(gca,'YTickLabel',[]);

Answer 1

[Star Strider]

Two problems:

First: ‘fs’ is the inverse of the sampling interval, or 1E+6.

Second, your code is correct although your plot is not. You can only plot to the Nyquist frequency (½ the sampling frequency), so your xlim call should be:

xlim([0 1e6/2])

Also, you need to normalise the fft result by dividing it by the length of your data vector:

X = abs(fft(x))/N;

and then multiply it by 2 to get the approximately correct amplitude in the plot.

Those changes result in a correct fft plot.

[Oscar Rodrigues]

You are the greatest human to ever exist. Thank you so much for your help. I wish you a wonderful life filled with blessings.

[Star Strider]

As always, my pleasure!

I very much appreciate your sentiments!