Tektronix RSA6100A Series, Help Manual

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General Signal Viewing > DPX Spectrum DPX Primer
Swept DPX
DPX Spectrum is not limited in span by its real-time bandwidth. Like the regular Spectrum display, DPX
Spectrum steps through multiple real-time frequency segments, building a wide-span display with line
traces and the bitmap (Option 200 only). See Figure 14.
Figure 14. Off-air ambient signals over a 1 GHz span in the swept DPX display.
The analyzer “dwells” in each frequency segment for one or more DPX frames, each containing the results
of up to 14,600 spectral transforms. Dwell time is adjustable, so you can monitor each segment of the
sweep for up to 100 seconds before moving to the next step. While dwelling in a segment, the probability
of intercept for signals within that frequency band is the same as in normal, real-time spans: 100% capture
of events as short as 10.3
μ sec.
A full pixel bitmap is created for every segment and compressed horizontally to the number of columns
needed for displaying the frequency segment. Compression is done by averaging pixel densities of the
points being combined together. The
fi nal swept bitmap contains a representation of the same pixel bitmap
resolution, just like the non-swept bitmaps. Line traces are also created in full for each segment, and then
horizontally compressed to the user-selected number of trace points for the full span.
A complex algorithm for determining the number and width of each frequency segment has been
implemented. The variables in the equation include user-adjustable control settings like Span, RBW, and
number of trace points, RF and IF optimization, and Acquisition BW. Installed hardware options also can
affect the span segmentation. The number of segments ranges from 10 to 50 for each 1 GHz in a sweep.
A helpful piece of information for operators is the actual Acquisition Bandwidth used for capturing each
segment. “Acq BW” is shown in the Acquire control panel on the Sampling Parameters tab. Acq BW is
typically set automatically by the instrument, based on the needs of all the open displays, but can also be
set manually. In either case, the displayed bandwidth is used for every frequency segment in the swept
DPX display, though in practice, the displayed portion of the segment is somewhat narrower than the
actual Acquisition BW, for performance reasons.
The entire instrument frequency range of many GHz can be covered in a DPX sweep. The Dwell Time
control sets the amount of time DPX spends in each segment. This control, circled in Figure 15, can be
set between 50 ms and 100 seconds.
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RSA6100A Series Real-Time Spectrum Analyzers Help