Tektronix RSA6100A Series, Help Manual

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General Signal Viewing > Common Controls for General
Signal Viewing Displays BW Tab
Setting Description
RBW Sets the Resolution Bandwidth value to be used in the spectrum analysis view. The
value is italicized when Auto is selected.
Auto When Auto is checked, the RBW is calculated as a percentage of the Span. Kaiser is
selected as the windowing method. When Auto is unchecked, the RBW is set by the user.
Selecting any Window other than Kaiser changes the RBW setting to manual.
Span/RBW ratio If Auto is checked, this value is used to calculate the RBW. If Auto is unchecked, this
setting is not selectable.
Filter Shape Speci fi es the windowing method used for the transform (when Auto is unchecked).
(Spectrum and Spectrogram displays only.)
VBW Adjusts the VBW (Video Bandwidth) value. (Spectrum and Spectrogram displays only.)
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Filter Shape Settings
In the analyzer, computationally ef fi cient discrete Fourier transform algorithms such as FFT (Fast Fourier
Transform) or CZT (Chirp-Z Transform) are generally employed to transform time-domain signals into
frequency-domain spectra. There is an assumption inherent in the mathematics of Discrete Fourier
Transforms that the data to be processed is a single period of a periodically repeating signal. The
discontinuities between successive frames will generally occur when the periodic extension is made to the
signal. These arti
fi cial discontinuities generate spurious responses not present in the original signal, which
can make it impossible to detect small signals in the presence of nearby large ones. This phenomenon is
called spectral leakage.
Applying a fi lter, such as Kaiser, to the signal to be transformed is an effective method to combat the
spectral leakage problem. Generally the fi lter has a bell shape. Multiplying the transform frame by the
fi lter function eliminates or reduces the discontinuities at the ends of the frame, however, at the expense of
increased RBW.
Filter Shape Characteristics
The choice of fi lter shape depends on its frequency response characteristics such as side-lobe level,
equivalent noise bandwidth and maximum amplitude error. Use the following guidelines to select the
best
fi lter shape.
Filter Shape Characteristics
Kaiser (RBW) Best side-lobe level, shape factor closest to the traditional Gaussian RBW.
-6dB RBW (MIL) These fi lters are speci fi ed for bandwidth at their -6 dB point, as required by military
EMI regulations.
CISPR These fi lters comply with the requirements speci fi ed in the P-CISPR 16 -1-1 document
for EMI measurements.
Blackman-Harris 4B Good side-lobe level.
Uniform (None) Best frequency resolution, poor side-lobe level and amplitude accuracy.
FlatTop Best amplitude accuracy, best representation of brief events captured near the beginning
or end of the time-domain data frame, poor frequency resolution.
Hanning Good frequency resolution, high side-lobe roll-off rate.
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RSA6100A Series Real-Time Spectrum Analyzers Help