FFT with non sinusoidal signal

2 次查看（过去 30 天）
Edoardo Matteo Marchica
编辑： Stephan 2018-4-23
Hi, I have to obtain the frequency analysis of a discrete time signal (current). I'll attach .mat of this signal.
The code I used is the following:
clear all
close all
clc
Fs = 10000;
Ts = 1/Fs;
t = 0 : 1/Fs : 2*pi/(2*pi*50) - 1/Fs;
theta = 2*pi*50*t;
Xt = i1;
%Transformation
n = 2^nextpow2(length(Xt));
Y=fft(Xt,n); %FFT
df=Fs/length(Y); %frequency resolution
f=(0:1:length(Y)/2)*df; %frequency axis
figure
subplot(3,1,1);
M=abs(Y)/length(Xt)*2; %amplitude spectrum
M_rounded = int16(M(1:size(f, 2))); %Limit the frequency range
ind = find(M_rounded ~= 0);
stem(f(ind), M(ind), 'LineWidth', 0.5);
xlim([0 350]);
grid on;
xlabel('Frequency (Hz)')
ylabel('Magnitude');
subplot(3,1,2);
P=angle(Y)*180/pi; %phase spectrum (in deg.)
stem(f(ind), P(ind), 'LineWidth', 0.5);
xlim([0 350]);
ylim([-100 100]);
grid on;
xlabel('Frequency (Hz)');
ylabel('Phase (degree)');
subplot(3,1,3)
plot(t,i1)
And it does not work. Can someone help me?
PS: sorry for my bad english

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回答（1 个）

Stephan
Stephan 2018-4-23
编辑：Stephan 2018-4-23
Hello,
When the code starts, you run the following command:
clear all
This command deletes your data in the Matlab workspace. Nowhere in your code do you import the .mat file of your signal. So there is nothing that the code can do due to missing data ...
Either you do it this way (provided you have previously inserted the data in the Matlab workspace):
%clear all
or you type an additionally line of code after your 3 cleaning-commands as follows:
load ('name_of_your_data_file.mat')
whatever the name of your file is.
After doing that, the data is loaded into the Matlab workspace and your code works on my Matlab.
best regards
Stephan

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