Rigol DS1000CA series Guía de usuario descargar pdf (Pagina 44)

RIGOL

User‟s Guide for DS1000CA Series

2-16

2. Selecting an FFT Window

Oscilloscope record the FFT change for a limit time assume that YT waveform

repeat ceaselessly. If cycle is integer, YT waveform voltage is the same at

starting and ending point, and waveform is consecutive. Contrary, If cycle is

non-integer, the voltage is different at starting and ending point, leading to the

high frequency instantaneous intermit, which is called “leak”. To avoid leak,

multiply a window function to force the value is 0 at starting and ending point.

DS1000CA provides four FFT functions with different feature, which are need to

be selected according to measuring waveform.

Table 2-8 FFT Windows

Window

Features

Best for measuring

Rectangle

Best frequency resolution

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

Better frequency, poorer

magnitude accuracy than

Rectangular.

Sine, periodic, and narrow-band

random noise.

Hamming

Hamming has slightly

better frequency

resolution than Hanning.

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.

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Rigol DS1000CA series Guía de usuario Pagina 44

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