Video filtering
In some analyzers a low-pass filter is included between the detector and the
display to smooth the noise level—in some cases revealing low-level signals that
might otherwise be obscured. Other analyzers are equipped with a “video
averaging” feature. This lets you average successive traces. Because video filtering
and video averaging both smooth the noise floor, the results of video averaging are
often similar to a single trace with video filtering.
Video averaging with the 89400 series vector signal analyzers is actually a better
approximation of noise than a video filtered-trace, since a series of averaged
measurements will reveal a complete frequency span much faster than the slower
progression of a single, video-filtered trace. However averaging, like video filtering,
does slow down a measurement.
Frequency span
Full-span measurements let you view the entire available frequency spectrum on
one display. With the 89410A, for example, full-span measurements extend from 0
Hz to 10 MHz. Measurements with spans that start at 0 Hz are often called
baseband measurements.
Alternatively, you may wish to view smaller slices of the frequency spectrum. You
can select any number of different spans and position these spans where you want
by specifying their start or center frequencies. This process of viewing smaller
spans is sometimes called zooming or band-selectable analysis. You can control
the frequency span examined by specifying a center frequency and a span size.
Alternatively, you can specify a start and a stop frequency to define a particular
frequency span.
In the 89400 series analyzers the sample rate is adjusted, based on the span, to
achieve the desired information bandwidth.
Fundamental Measurement Interactions
19 - 3
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