Plotting FFT Spectrum using Square Wave

14 次查看（过去 30 天）
Oscar Rodrigues
Oscar Rodrigues 2019-7-7
评论： Star Strider 2019-7-7
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',[]);

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2019-7-7
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.
  2 个评论
Oscar Rodrigues
Oscar Rodrigues 2019-7-7
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
Star Strider 2019-7-7
As always, my pleasure!
I very much appreciate your sentiments!

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Fourier Analysis and Filtering 的更多信息

标签

Community Treasure Hunt

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

Start Hunting!

Translated by