how to use FFT in matlab using imported data in time domain excel file

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Passband Modulation
评论： Gagan Jain 2021-12-17
i have some polymers characterized by transmission terahertz time domain spectroscopy (THz-TDS).

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Wayne King
Wayne King 2012-8-12
Import the data into MATLAB using xlsread()
Your data will be a Nx2 matrix in MATLAB with the first column the time data and the second column the data you want to Fourier transform.
So for example:
[X,TXT,RAW] = xlsread('yourfile.xls');
xdft = fft(X(:,2));

更多回答（2 个）

Wayne King
Wayne King 2012-8-12
编辑：Wayne King 2012-8-12
There is a slight variation depending on whether you have an even or odd number of samples in your data.
Even length:
xdft = fft(X(:,2));
% sampling interval -- assuming equal sampling
DT = X(2,1)-X(1,1);
% sampling frequency
Fs = 1/DT;
DF = Fs/size(X,1);
freq = 0:DF:Fs/2;
xdft = xdft(1:length(xdft)/2+1);
plot(freq,abs(xdft))
Odd length
xdft = fft(X(:,2));
% sampling interval -- assuming equal sampling
DT = X(2,1)-X(1,1);
% sampling frequency
Fs = 1/DT;
DF = Fs/size(X,1);
freq = 0:DF:Fs/2;
xdft = xdft(1:round(length(x)/2));
plot(freq,abs(xdft))
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显示 2更早的评论
Mathias
Mathias 2017-2-25
This doesn't seem to work for me. But why not just use the length of freq?
xdft = xdft(1:length(freq));
Sahaphol Hamanee
Sahaphol Hamanee 2018-2-14
编辑：Sahaphol Hamanee 2018-2-14
Hi Wayne King, thank you for your guidance. May I ask what DF = Fs/size(X,1); is for? What is the meaning of it? It is the only thing I didn´t understand.
Best Regards

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Wayne King
Wayne King 2012-8-13
编辑：Wayne King 2012-8-13
To get the phase, use angle()
phi = angle(xdft);
To export the frequencies and magnitudes back to Excel, place them in a matrix.
Xdftmatrix = [freq' abs(xdft)];
then use xlswrite

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