How to find phase and frequency spectrum of signal?

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Ihor
Ihor 2023-11-17
评论： Paul 2023-11-17
I have a signal:
t = -2:0.01:2;
x = zeros(size(t));
x(t >= -2 & t < -1) = -1;
x(t >= 0 & t <= 2) = -1;
how I can find frequency and phase spectrum of this signal? I need to plot all of it.

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回答（1 个）

Star Strider
Star Strider 2023-11-17
Ran in:
A one-sided fft —
t = -2:0.01:2;
x = zeros(size(t));
x(t >= -2 & t < -1) = -1;
x(t >= 0 & t <= 2) = -1;
figure
plot(t, x)
grid
xlabel('t')
ylabel('x')
title('Time Domain Plot of ‘x(t)’')
axis('padded')
Fs = 1/mean(diff(t));
Fn = Fs/2;
L = numel(t);
NFFT = 2^nextpow2(L);
FTx = fft(x(:).*hann(L), NFFT)/L;
Fv = linspace(0, 1, NFFT/2+1)*Fn;
Iv = 1:numel(Fv);
figure
tiledlayout(2,1)
nexttile
plot(Fv, abs(FTx(Iv))*2)
grid
ylabel('Magnitude (absolute)')
nexttile
plot(Fv, unwrap(angle(FTx(Iv))))
grid
xlabel('Frequency (cycles/(time unit))')
ylabel('Phase (rad)')
sgtitle('One-Sided Fourier Transform of ‘x(t)’')
Make appropriate changes to get the result you want.
.
  1 个评论
Paul
Paul 2023-11-17
Doesn't some adjustment need to be made to the phase to account for the fact that the signal "starts" in negative time, but fft assumes the the first point in the input corresponds to t = 0?

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