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From: thisisme on 17 Apr 2010 15:25
Hi, I have a time domain data file which is acquired by a 100MSample digitizer. The data file has 10000 samples of the data. I only want to see the spectral content of a part of the data. I have the following code. I will appreciate if someone tells me this is alright or am I missing out on something or doing something wrong.:

clear all;

Fs = 100000000; % Sampling frequency
T = 1/Fs; % Sample time
L = 4096; % Length of signal
%t = (0:L-1)*T; % Time vector
filenames = dir;


load tdmfile;
start_point = 1600;
end_point = 5595; % start point and end point are taken so that they match the
%value of L so that it doesn't pad zeros to the data
% start_point =1650;
% end_point = 2161;

t = tdmfile(start_point:end_point, 1);
x = tdmfile(start_point:end_point, 2);




NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(x,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);

% Plot single-sided amplitude spectrum.

subplot(2,1,1)

plot(t,x);
grid on
axis([min(t) max(t) min(x) max(x)])
title((filenames(i,1).name));

subplot(2,1,2)

plot(f,2*abs(Y(1:NFFT/2+1)))
%plot(f,20*log10(Y(1:NFFT/2+1)))
grid on
% saveas(figure(i),sprintf('img%03d',i),'jpg')

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Next: alligning columns in a file