Rigol DS1074B Guide de l'utilisateur télécharger pdf (Page 45)

RIGOL

User’s Guide for DS1000E, DS1000D Series

2-15

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:

FFT Resolution: the quotient between sampling rate and number of FFT

points. With a fixed FFT points, the lower sampling rate results in better

resolution.

Nyquist Frequency

The highest frequency that any real-time digitizing 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.

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Rigol DS1074B Guide de l'utilisateur Page 45

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