User`s guide
units
Dimensions on the measured quantities. Units usually refer to amplitude quantities because
they can be changed. In spectrum analyzers with microprocessors, available units are dBm
(dB
relative to 1
mW
(milliwatt) dissipated in the nominal input impedance of the analyzer),
dBmV
(dB
relative to 1
mV
(millivolt)),
dBpV
(dB
relative to 1
pV>,
volts, and in some
analyzers watts.
update
To make existing information current; to bring information up to date.
upgrade
To improve the quality or extend the capability of an instrument or product. Enhancements
to upgrade the product. These enhancements can then be documented in an update
package.
variable persistence
A property of the display that allows the adjustment of the trace-fade rate which is created
by the display’s electron beam. It is a capability of purely analog displays which provides
flicker-free trace display regardless of sweep time.
vector display
The display type where the electron beam is directed so the image (consisting of trace,
graticule, and annotation) is written directly onto the display face. It is not created from a
series of dots as with the raster display.
video
A term describing the output of a spectrum analyzer’s envelope detector. The frequency
range extends from 0 Hz to a frequency that is typically well beyond the widest resolution
bandwidth available in the analyzer. However, the ultimate bandwidth of the video chain is
determined by the setting of the video filter.
video amplifier
A post-detection, dc-coupled amplifier that drives the vertical deflection plates of the
display. Refer also to video bandwidth and video filter.
video average
The digital averaging of spectrum analyzer trace information. It is available only on
analyzers with digital displays. Each point on the display is averaged independently
and the average is computed based on the number of sweeps selected by the user. The
averaging algorithm applies a factor to the amplitude value of a given point on the current
sweep
(l/n,
where n is the number of the current sweep); applies another factor to the
previously stored average [(n
-
l/n)]; and combines the two for a current average. After
the designated number of sweeps are completed, the factors remain constant, and the
display becomes a running average.
video bandwidth
The cut-off frequency (3
dB
point) of an adjustable low-pass filter in the video circuit.
When the video bandwidth is equal to or less than the resolution bandwidth, the video
circuit cannot fully respond to the more rapid fluctuations of the output of the envelope
detector. The result is a smoothing of the trace, or a reduction in the peak-to-peak
excursion, of broadband signals such as noise and pulsed RF when viewed in broadband
mode. The degree of averaging or smoothing is a function of the ratio of the video
bandwidth to the resolution bandwidth.
Glossary-l 7