Tektronix TDS1000- Uživatelský manuál stáhnout pdf (Strana 140)

Math FFT

122

TDS1000/2000-Series Digital Oscilloscope User Manual

The Math FFT function incl udes three FFT Window options. There is

a trade-off between frequency resolution and amplitude accuracy

with each type of window. What you want to measure and your

source signal charact eristics help you to determine which window to

use.

Window Measure Characteristics

Hanning Periodic

waveforms

Better frequency, poorer magnitude

accuracy than Flattop

Flattop Periodic

waveforms

Better magnitude, poorer frequency

accuracy than Hanning

Rectangular Pulses or

transients

Special-purpose window for waveforms that

do not have discontinuities. This is essential-

ly the same as no window

FFT Aliasing

Problems occur when the oscilloscope acquires a time-domain

waveform containing frequency com ponents that are greater than the

Nyquist frequency (refer to Nyquist Frequency on page 117). The

frequency components that a re a bove the Nyquist frequency are

undersampled, appearing as lower frequency components that “fold

back” around the Nyquist frequency. These incorrect components are

called aliases.

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Tektronix TDS1000- Uživatelský manuál Strana 140