我在matlab上执行了阶跃函数FFT，但仅获得了频谱的一侧(0到无穷大) [英] I did a step function FFT on matlab but only getting one side of the spectrum (0 to infinity)

问题描述

使用此代码，我只能得到从0到正无穷大的fft频谱的一半.我正在尝试沿y轴镜像此镜像，以使另一半与该对称的从0到负无穷大对称.

with this code i am only getting half og the fft spectrum from 0 to positive infinity . i am trying to mirror this along the y axis to get the other half which is symmetric to this one from 0 to negative infinity.

    Fs = 1000;   %sampling rate
    Ts = 1/Fs; %sampling time interval
    t = -10:Ts:10-Ts; %sampling period
    n = length(t); %number of samples
    y = heaviside(t)-heaviside(t-4); %the step curve

    matlabFFT = figure;  %create a new figure
    YfreqDomain = fft(y); %take the fft of our step funcion, y(t)
    y=abs(YfreqDomain);
    plot(y)
    xlabel('Sample Number')
    ylabel('Amplitude')
    title('Using the Matlab fft command')
    grid
    axis([-100,100,0,5000])

推荐答案

这是正常行为. FFT仅以正频率(0到Fs之间)返回频谱.您可以使用fftshift进行更正.零频率将位于x轴的中心.所以你应该使用

That's normal behaviour. The FFT returns the spectrum in positive frequencies only (between 0 and Fs). You can use fftshift to correct that. The zero frequency will then be at the center of the x axis. So you should use

plot(fftshift(y))
axis([-100+1e4,100+1e4,0,5000])

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