My Matlab FFT plot keeps showing the mirrored values of my frequency of interest. In this example I am looking for 250Hz with a 3200Hz sampling freq. The FFT plots my value at 266Hz as well as 1330 Hz. I assume my sampling freq is a little off which is why it isn't exactly at 250Hz. Matlab code is below, any help is appreciated.
% Tmax = (N-1)*Ts
% largest freq = Fs/2
% smalles = -fs/2
fid = fopen('250Hz.bin');
AA = fread(fid, 'short');
length(AA);
flenbytes = ftell(fid);
flenshorts = floor(flenbytes/2);
FF = floor(flenshorts/16)*16;
fseek(fid,0, 'bof');
BB = fread(fid, [8 (FF/8)], 'short');
CC = BB';
DataSet = CC ./2^3;
Z1Axis = DataSet(:,4);
N = length(DataSet)
Fs = 3200;
ts = 1/Fs;
tmax = (N-1)*ts;
t = 0:ts:tmax; %start at 0 increment by ts up to tmax
plot(t,Z1Axis)
f = (0:N-1)*(Fs/N)/2; % start with -Fs/2, increment by Fs/(N-1), goes to Fs/2
z = fft(Z1Axis);
%zreal =
%plot(f,z)
plot(f,abs(z));