Selecting an FFT window
Windows reduce spectral leakage in the FFT spectrum. The FFT assumes that the
YT waveform repeats forever. With an integral number of cycles (1, 2, 3, ...), the
YT waveform starts and ends at the same amplitude and there are no
discontinuities in the signal shape.
A non-integral number of cycles in the YT waveform causes the signal start and
end points to be at different amplitudes. The transitions between the start and end
points cause discontinuities in the signal that introduce high-frequency transients.
Applying a window to the YT waveform changes the waveform so that the start
and stop values are close to each other, reducing the discontinuities.
FFT
56 TBS1000B and TBS1000B-EDU Series Oscilloscopes User Manual