Problem with frequency axis during Fourier Transform of Gaussian Pulse
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Hello, I noticed that whenever I change dt(sampling time) the bandwidth of FFT Gaussian changes. Smaller dt will have wider bandwidth.
- Why is this happening? Doesn't smaller dt just allows more points for better signal sampling in time domain?
clc
clear all
close all
dt=15e-12;
t=0:dt:2e-9;
tao = .5e-9;
nfft = length(t);
%frequency spectrum
fs = 1/dt;
df = fs/(nfft-1);
f=(-fs/2):df:(fs/2);
sigma1=.1E-9;
x1=((t-tao)/sigma1).*((t-tao)/sigma1);
G1=(1/(sqrt(6.28)*sigma1)).*exp(.5.*(-x1));
%Fourier Transform
G7 = fftshift(abs(fft(G1)));
plot(f/1E9,G7)
xlim([-50 50]);
Thanks,
1 Comment
Rick Rosson
on 3 Mar 2014
Edited: Rick Rosson
on 3 Mar 2014
Please post screen shots of the spectrum for each of two different values of dt.
Answers (1)
Rick Rosson
on 3 Mar 2014
Edited: Rick Rosson
on 3 Mar 2014
A few minor tweaks:
t = 0:dt:2e-9-dt;
df = fs/nfft;
f = -fs/2:df:fs/2-df;
2 Comments
Rick Rosson
on 4 Mar 2014
Yes, that is correct. If you change dt, then that also changes fs, and that will change the range of frequencies over which the Fourier spectrum is defined. So it is crucial that when you change dt, you recompute fs and everything else that depends on dt.
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