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270 Keysight InfiniiVision DSOX1204A/G Oscilloscopes Programmer's Guide

15 :FFT Commands

:FFT:WINDow

(see page 798)

Command Syntax

:FFT:WINDow <window>

<window> ::= {RECTangular | HANNing | FLATtop | BHARris}

The :FFT:WINDow command allows the selection of four different windowing

transforms or operations for the FFT (Fast Fourier Transform) function.

The FFT operation assumes that the time record repeats. Unless an integral

number of sampled waveform cycles exist in the record, a discontinuity is created

between the end of one record and the beginning of the next. This discontinuity

introduces additional frequency components about the peaks into the spectrum.

This is referred to as leakage. To minimize leakage, windows that approach zero

smoothly at the start and end of the record are employed as filters to the FFTs.

Each window is useful for certain classes of input signals.

• RECTangular — useful for transient signals, and signals where there are an

integral number of cycles in the time record.

• HANNing — useful for frequency resolution and general purpose use. It is good

for resolving two frequencies that are close together, or for making frequency

measurements. This is the default window.

• FLATtop — best for making accurate amplitude measurements of frequency

peaks.

• BHARris (Blackman-Harris) — reduces time resolution compared to the

rectangular window, but it improves the capacity to detect smaller impulses

due to lower secondary lobes (provides minimal spectral leakage).

Query Syntax

:FFT:WINDow?

The :FFT:WINDow? query returns the value of the window selected for the FFT

function.

Return Format

<window> ::= {RECT | HANN | FLAT | BHAR}

Keysight Technologies InfiniiVision DSOX1204G User Manual

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