Agilent Technologies Infiniium 90000 Q-Series, Programmer'S Manual

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336 Agilent Infiniium 90000 Series Oscilloscopes Programmer's Reference
17
Function Commands
:FUNCtion<F>:FFT:WINDow
Command
:FUNCtion<F>:FFT:WINDow {RECTangular | HANNing | FLATtop
| BHARris | HAMMing}
The :FUNCtion<F>:FFT:WINDow command sets the window type for the
FFT function.
The FFT function assumes that the time record repeats. Unless there is an
integral number of cycles of the sampled waveform in the record, a
discontinuity is created at the beginning of the record. This introduces
additional frequency components into the spectrum about the actual peaks,
which is referred to as spectral leakage. To minimize spectral leakage,
windows that approach zero smoothly at the beginning and end of the
record are employed as filters to the FFTs. Each window is useful for
certain classes of input waveforms.
• RECTangular — is essentially no window, and all points are multiplied
by 1. This window is useful for transient waveforms and waveforms
where there are an integral number of cycles in the time record.
• HANNing — is useful for frequency resolution and general purpose use.
It is good for resolving two frequencies that are close together, or for
making frequency measurements.
• FLATtop — is best for making accurate amplitude measurements of
frequency peaks.
• BHARris — (Blackman- Harris) is best used when you want to looks at
signals with a strong interference component that is fairly distant from
the frequency you want to see. It can be used as a general purpose
window as its main lobe is not too wide (decent frequency
discrimination) and the side lobes drop off by 90 dB.
• HAMMing —is a "raised cosine" function like the HANNing window but
with different coefficients. It has slightly better frequency resolution
than the HANNing window.
<F>
An integer, 1- 16, representing the selected function. This command
presently selects all functions, regardless of which integer (1- 16) is passed.
Example
This example sets the window type for the FFT function to RECTangular.
myScope.WriteString ":FUNCtion1:FFT:WINDow RECTangular"
Query
:FUNCtion<F>:FFT:WINDow?
The :FUNCtion<F>:FFT:WINDow? query returns the current selected
window for the FFT function.
Returned Format
[:FUNCtion<F>:FFT:WINDow] {RECTangular | HANNing | FLATtop
| BHARris | HAMMing}<NL>