Analyze Trace Bandwidth
Other topics about Analysis and Processing of Result
The E4990A can automatically derive the parameters called bandwidth, center value, Q value, peak,DL, and DR from the measurement trace.
At the instant when the trace bandwidth analysis function is turned On and at the completion of each subsequent sweep, cutoff points are searched for on the sweep parameter value axis, starting from the main marker position at that time and advancing in both directions. When two cutoff points are detected, six parameters (bandwidth (width), center value (center), Q, peak (peak), DL, and DR) are derived from the data at those points and displayed in the Marker Statistics/Trace Bandwidth Analysis Result field on the right of the screen.
- The peak (peak), one of the six parameters displayed on the screen as trace bandwidth analysis results, is the first position of the main marker itself. Therefore, before executing the trace bandwidth analysis, use the peak search function and so on to move the main marker to the peak on the trace as necessary. The cutoff points are searched for according to the definition specified by the user. The definitions of the six parameters displayed on the screen as the final results also vary depending on the delta marker mode selected at the time.
Table below shows the definition of each parameter in the trace bandwidth analysis.
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Cutoff point
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Two points having the predefined measurement parameter value that are searched for and detected from the main marker position to both ends on the trace. You define the measurement parameter value of the cutoff points by selecting, assuming that the measurement parameter value of the main marker position is MKRVAL, ,  ,  or a user entered value (fixed value). At the detected cutoff points, the sub-markers numbered 2 and 3 will be placed.
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Bandwidth:
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Indicates the interval of sweep parameter values at two cutoff points. This definition does not depend on the marker mode.
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Center:
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Indicates a midpoint between the sweep parameter values at two cutoff points. It serves as a relative value with reference to the fixed marker only when the fixed marker is present.
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Q
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Indicates value Q obtained from two cutoff points (Center/Width).
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Peak:
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Indicates the measurement parameter value at the position of the main marker (marker 0). However, it indicates a relative value with reference to the fixed marker only when the fixed marker is present. When the main marker is moved to the peak by using the peak search function, that peak is displayed at this position.
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DL
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Indicates the length of the sweep parameter from the sweep center value to the cutoff point on the left. However, it indicates the length of the sweep parameter from the sweep parameter value of the fixed D marker to the cutoff point on the left only when the fixed D marker is present.
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DR
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Indicates the length of the sweep parameter from the sweep center value to the cutoff point on the right. However, it indicates the length of the sweep parameter from the sweep parameter value of the fixed D marker to the cutoff point on the right only when the fixed D marker is present.
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When trace bandwidth analysis is performed, the Keysight E4990A searches for the cutoff points on both sides with respect to the sweep parameter shaft starting from the main marker position. The cutoff point used for this search is defined by the following steps:
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Activate the trace for which you want to analyze trace bandwidth.
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Press the Marker Search key to display the Marker Search menu.
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Press Widths Def to display the trace bandwidth analysis definition menu.
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Select the definition of the cutoff point in trace bandwidth analysis from the following:
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MkrVal/sqrt(2)
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MkrVal*sqrt(2)
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MkrVal/2
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MkrVal*2
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MKRVAL x 2
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MkrVal-Fixed
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MKRVAL - fixed value
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MkrVal+Fixed
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MKRVAL + fixed value
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Fixed Value
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Fixed value specified by numerical value
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1 MKRVAL: Indicates the measurement parameter value (measurement) at the position of the main marker (marker 0).
Fixed value: Indicates the absolute value of the measurement parameter if there is no D marker; it is a relative value with reference to the tracking D marker tracking (D marker that moves with the main marker) is present and a relative value with reference to the fixed D marker if the fixed marker is present.
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Press the BW Fixed Value, and input the desired bandwidth value.
The following describes the steps to implement trace bandwidth analysis:
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Activate the trace used to implement trace bandwidth analysis.
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Display the main marker and move it to the desired position on the trace to analyze trace bandwidth. To move the main marker to the peak of the trace, see Search the maximum/minimum peak.
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Press the Marker Search key to display the Marker Search menu.
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Press Bandwidth > ON|OFF to turn On or Off the trace bandwidth analysis function.
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Once the trace bandwidth analysis function is turned On, the bandwidth (width), center value (center), Q (Q), peak (peak), DL(DL), and DR(DR) are displayed in the Marker Statistics/Trace Bandwidth Analysis Result area on the top-left of the screen.
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If the trace bandwidth analysis function is turned On, the straight line showing the cutoff line is displayed parallel to the sweep parameter axis.
Cutoff point re-search does not cause the main marker to move, so it does not affect the peak value. If the two cutoff points cannot be found by trace bandwidth analysis, the message Target Value Not Found will appear at the bottom left side of the bar of the screen. If a partial search range is specified by following Searching for Positions that Match Specified Criteria, trace bandwidth analysis will be executed within that range. Even if the trace bandwidth analysis function is turned Off, the marker used for analysis will not disappear from the screen.