Agilent Technologies InfiniiVision 4000 X-Series, Programmer'S Manual

Page: 351 / 1352

:FUNCtion<m> Commands
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Agilent InfiniiVision 4000 X-Series Oscilloscopes Programmer's Guide 351
:FUNCtion<m>[:FFT]:WINDow
(see page 1208 )
Command Syntax
:FUNCtion<m>[:FFT]:WINDow <window>
<m> ::= 1-4 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 • "Introduction to :FUNCtion<m> Commands" on page 340