What Is A Detector And Why Is One Needed - Agilent Technologies 89410A Operator's Manual

Fundamental Measurement Interactions

What is a detector and why is one needed

The measurement results that you view on the CRT screen are actually made up of
51 to 3201 evenly-spaced discrete frequency points. For spectrum measurements,
these points represent the range of frequencies that the analyzer evaluates during
each frequency sweep—extending from the currently-selected start frequency to
the currently-selected stop frequency. The analyzer always uses the number of
points you have selected to represent measurement data, regardless of selected
frequency span or measurement type.
During spectrum measurements, the analyzer evaluates all frequencies within its
displayed frequency span but it determines the number of points to display
depending on the number of frequency points you have selected. The interval
between frequency points represents one displayed point. Between two frequency
points the signal may rise and fall a number of times. A detector determines what
signal level to display for each interval.
For example, with narrow resolution bandwidths the stepped FFT measurements
can result in more measurement points than were requested. When this occurs a
data reduction must occur. The process of reducing the data is called detection.
Detection works by combining the results of several FFT bins into a single display
point. In the process of detection some information is lost. For this reason several
detectors are provided, each optimized for a different purpose.
The peak, normal, or sample detector uses its own algorithm to find a suitable
spectral point between the nominal frequencies that define a pair of frequency
points. It transfers the amplitude of this spectral point to a nearby display point.
The analyzer moves the detected point between two frequency points to the
leftmost point for each pair of frequency points. For more information on how
each detector type functions, display the relevant online help topics.
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