Rigol DS1000D Manuel d'utilisateur télécharger pdf (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.

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Rigol DS1000D Manuel d'utilisateur Page 42

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