Question

clear all;

Fs=100; %sampling rate

t=-10:(1/Fs):10;

for i=1:20*Fs+1

if -10<t(i) && t(i)<-9
x(i)= -1;

elseif -9<t(i) && t(i)<-8

x(i)=1;

elseif i>2*Fs+1

x(i)=x(i-(2*Fs));

上面显示的

是矩形函数的代码，其域[-10 10]和周期2

这是我的positiveFFT函数

function [X,freq]=positiveFFT(x,Fs)
N=length(x); %get the number of points
k=0:N-1;     %create a vector from 0 to N-1
T=N/Fs;      %get the frequency interval
freq=k/T;    %create the frequency range
X=fft(x)/N*2; % normalize the data

%only want the first half of the FFT, since it is redundant
cutOff = ceil(N/2); 

%take only the first half of the spectrum
X = X(1:cutOff);
freq = freq(1:cutOff);`

通过这样做，我制作了这个矩形波的幅度谱，但只有当频率为正时。

如何绘制包含负频率的整个幅度谱？

Answer 1

如果我理解正确，您需要获得频率为-Fs / 2到Fs / 2的矢量以及相应的频谱幅度。如果是这样，您应该使用fftshift，例如：

N=length(x); %get the number of points
k=0:N-1;     %create a vector from 0 to N-1
T=N/Fs;      %get the frequency interval
freq=fftshift(k/T);    %create the frequency range
X=fftshift(fft(x))/N*2; % normalize the data

怎样才能在matlab中使用负频率进行傅里叶变换？

1 个答案: