Reference
FFT window C haracteristics Best for measuring
Blackman-Har
ris
Best magnitud
e, worst at
resolving frequencies.
Predominantly single frequency
waveforms to look for higher order
harmonics.
Hamming, Hanning
Better frequ
ency, poorer
magnitude accuracy than
Rectangular. Hamming
has slightl
y better
frequency resolution
than Hanning.
Sine, period
ic, and narrow-band
random noise.
Transients or bursts where the signal
levels befo
re and after the event are
significantly different.
Rectangular
Best frequency, worst
magnitude
resolution.
This is essentially the
same as no window.
Transients or bursts where the signal
levels before and after the event are
nearly equ
al.
Equal-amplitude sine waves with
frequencies that are very close.
Broad-ba
nd random noise with a
relatively slow varying spectrum.
Aliasin
g. Problems occur when the oscilloscope acquires a signal containing
frequency components that are greater than the Nyquist frequency (1/2 the sample
rate). The frequency components that are above the Nyquist frequency are
undersampled and appear to "fold back" around the right edge of the graticule,
showing as lower frequency components in the FFT waveform. These incorrect
components are called aliases.
76 TDS3000C Series Oscilloscope User Manual
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