Rigol VS5000 Series User Manual page 51

RIGOL
Selecting a FFT Window
VS5000 series digital oscilloscopes provide four FFT window functions. Each window
is a trade-off between frequency resolution and amplitude accuracy. It depends on
the desired measurements and source signals characteristics to determine the
window to use. Use the following guidelines to select the best window.
Table 2-7 FFT Windows description
Window
Rectangle
Hanning
Hamming
Blackman
Key points:
FFT Resolution
With a fixed FFT points, the lower sampling rate results in better resolution.
Nyquist Frequency
The highest frequency that any real-time digital oscilloscope can acquire
without aliasing. It's normally half of the sample rate. This frequency is called
the Nyquist frequency. Frequency above the Nyquist frequency will be under
sampled, causing a situation known as aliasing.
© 2008 RIGOL Technologies, Inc.
Features
Best frequency resolution
and worst
resolution. This is essentially
the same as no window.
Better frequency,
magnitude accuracy than
Rectangular.
Hamming has slightly
better frequency resolution
than Hanning.
Best magnitude, worst
frequency resolution.
User's Guide for VS5000 Series
Transients or bursts, the signal
levels before and after the event
are nearly equal.
magnitude
Equal-amplitude sine waves with
fixed frequencies.
Broadband random noise with a
relatively slow varying spectrum.
poorer Sine, periodic, and narrow-band
random noise.
Transients or bursts where the
signal levels before and after the
events are significantly different.
Single frequency waveforms, to
find higher order harmonics.
Best for measuring
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