RIGOL DS1000D User Manual

Page 42

RIGOL

User’s Guide for DS1000E, DS1000D Series

2-12

2. Selecting an FFT Window

The oscilloscopes provide four FFT windows. Each window is a trade-off between
frequency resolution and amplitude accuracy. What you want to measure and your
source signals characteristics help determine which window to use. Use the
following guidelines to select the best window.

Table 2- 7 FFT Windows

Window

Features

Best for measuring

Rectangle

Best frequency
Resolution and worst
magnitude resolution.
This is essentially the
same as no window.

Transients or bursts, the signal
levels before and after the event
are nearly equal.
Equal-amplitude sine waves with
fixed frequencies.
Broadband random noise with a
relatively slow varying spectrum.

Hanning
Hamming

Better frequency,
poorer magnitude
accuracy than
Rectangular.
Hamming has slightly
better frequency
resolution than
Hanning.

Sine, periodic, and narrow-band
random noise.
Transients or bursts where the
signal levels before and after the
events are significantly different.

Blackman

Best magnitude, worst
frequency resolution.

Single frequency waveforms, to
Find higher order harmonics.

Key points for FFT

Signals that have a DC component or offset can cause incorrect FFT waveform

component magnitude values. To minimize the DC component, choose AC

Coupling on the source signal.

To reduce random noise and aliases components in repetitive or single-shot

events, set the oscilloscope acquisition mode to average.

To display FFT waveforms with a large dynamic range, use the dBVrms scale. The

dBVrms scale displays component magnitudes using a log scale.

This manual is related to the following products:

DS1000E