FFT of a Signal

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Harry
Harry el 26 de Feb. de 2017
Comentada: Star Strider el 27 de Feb. de 2017
Hi, I would like to take the FFT of a signal but for some reason I do something wrong.
May someone could help me out?
I would like to see the FFT Spectrum for 2 seconds.
I attached the Excel file and the code.
Thanks!

Respuesta aceptada

Star Strider
Star Strider el 26 de Feb. de 2017
The constant (‘direct current’ or ‘d-c’ 0 Hz) offset is hiding the rest of your spectrum. This is a common problem, and since removing the constant offset does not affect the rest of your signal (and you can easily recover it if needed, since it is the mean of your signal), remove it before calculating the fft to see the rest of your spectrum.
This works:
[d,s] = xlsread('Good State.xls');
Time = d(:,1);
Good = d(:,2);
L = size(d,1); % Vector Length
Ts = mean(diff(Time)); % Sampling Interval (Assume ‘seconds’)
Fs = 1/Ts; % Sampling Frequency (Assume ‘Hz’)
Fn = Fs/2; % Nyquist Frequency (Assume ‘Hz’)
Good = Good - mean(Good); % Remove D-C (Constant) Offset
Y = fft(Good)/L; % Scaled Two-Sided Discrete Fourier Transform
Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector
Iv = 1:length(Fv); % Index Vector For Plot
figure(1)
plot(Fv, 2*abs(Y(Iv)))
grid
xlabel('Frequency')
ylabel('Magnitude')

Más respuestas (1)

Harry
Harry el 26 de Feb. de 2017
Brilliant! Thank you!
  5 comentarios
Harry
Harry el 27 de Feb. de 2017
Nice one!
Much appreciated!
Thank you
Star Strider
Star Strider el 27 de Feb. de 2017
My pleasure!

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