Operating instructions

University of Saskatchewan
Electrical Engineering Laboratory Equipment Manual
Energy is smeared throughout the frequency spectrum if the signal is not
periodic. Windowing solves this problem. Windowing functions taper off to zero at the
start and the end.
( Agilent Technologies, 2000 )
The Window submenu is found in the Measure menu. The Uniform window is
basically no windowing. It is used for pulses and transients which are shorter then the
time record. The Flattop window is used for magnitude measurements of continuous
signals. The Hanning window is used for frequency measurements of continuous
signals. The BMH ( Blackman-Harris ) window has the best selectivity because of it’s
narrow mainlobe and a fast roll-off.
Note: A input signal is at 10.1 KHz. The analyzer displays the peak at 10 KHz.
This is because the FFT only results in 400 discrete frequency bins. The signal peak is
always wider than with no windowing. This reduces the selectivity of the spectrum.
Signals that are not at exact bin frequencies will have a reduced amplitude. This is
because window functions attenuate the amplitude between bins.