:FUNCtion<m> Commands 18
Keysight InfiniiVision 4000 X-Series Oscilloscopes Programmer's Guide 409
:FUNCtion<m>[:FFT]:WINDow
(see page 1428)
Command Syntax
:FUNCtion<m>[:FFT]:WINDow <window>
<m> ::= 1 to (# math functions) in NR1 format
<window> ::= {RECTangular | HANNing | FLATtop | BHARris}
The :FUNCtion<m>[: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
:FUNCtion<m>[:FFT]:WINDow?
The :FUNCtion<m>[:FFT]:WINDow? query returns the value of the window selected
for the FFT function.
Return Format
<window><NL>
<window> ::= {RECT | HANN | FLAT | BHAR}
See Also • ":FUNCtion<m>[:FFT]:GATE" on page 405
• "Introduction to :FUNCtion<m> Commands" on page 393
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