When performing a DFT on a small sample, why is one of the frequencies found due to the length of the sample?

For example if I perform a DFT on the function cos(6*pi*t) over the range t=0 to t=0.2 sec, with a sampling frequency of 1000Hz, the FFT in MATLAB results in a frequency of 5 Hz.  This is due to...

02 February 2017 9,703 3 View