Hello

I want to use fft in MATLAB to analize some exprimental data saved as an excell file. my code:

A=xlsread('Book.xls'); G=A'; x=G(2, : );
N=length(x);
F=[-N/2:N/2-1]/N;
X = abs(fft(x-mean(x),N))
X = fftshift(X);
plot(F,X)

But it plots a graph with a large 0Hz wrong component, my true frequency is about 395Hz and it is not shown in the plotted graph. Please tell me what is wrong.

Any help would be appreciated.