# How to do FFT on I,Q data

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Ankit il 16 Ott 2023
Commentato: William Rose il 15 Feb 2024 alle 18:52
I am Working on a climate orbiter satellite data, from there i have extracted the In_Phase and Quadrature_Phase in decimal form now wanted to do further processing such as FFT , PSD etc.
Can Someone help how to do FFT on that type of data?
Note: I have Very large dataset which is about 144crores but i have divided it into chuncks of files which is about 8 lakh each.
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### Risposte (1)

William Rose il 16 Ott 2023
Let's assume you have read in data from a two-column file. Column 1 is in-phase, column 2 is quadrature.
N=256;
fs=100e6; % sampling rate (Hz)
t=(0:N-1)/fs;
data=randn(N,2);
Combine the ccolumns to make a single vector of complex numbers
The second column is multiplied by 1i, which is pre-defined as sqrt(-1).
x=data(:,1)+1i*data(:,2);
Now do FFTs or compute power spectra in the usual way. The only difference is that, since x(t) is complex, the FFTs and spectra will not be conjugate-symmetric around the Nyquist frequency. (If you prefer to think of positive and negative frequencies, then the spectra will not be conjugate-symmetric around f=0.)
X=fft(x);
f=(0:N-1)*fs/N;
Plot results
figure; subplot(311)
plot(t,data(:,1),'-r.',t,data(:,2),'-b.'); grid on; xlabel('Time (s)')
subplot(312);
plot(f,abs(X),'-g.'); grid on; xlabel('Frequency (Hz)')
ylabel('|X(f)|'); title('FFT')
subplot(313);
plot(f,unwrap(phase(X))*180/pi,'-g.'); grid on; xlabel('Frequency (Hz)')
ylabel('phase(X) (deg)'); title('FFT')
Good luck.
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William Rose il 14 Feb 2024 alle 4:35
@silvia cano, I have no idea.
William Rose il 15 Feb 2024 alle 18:52
@silvia cano, since you are asking a new question,
I recommend that you post your question as a new quesiton on Matlab Answers. Include the data that you have that relates to range.

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