HP 8591C, Руководство пользователя, Страница: 350 / 373

video
A term describing the output of an 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
Video is also a term describing the television
signal composed of visual carriers/modulation.
video average
The digital averaging of 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
where
n
is the number of the current sweep); applies another factor to the
previously stored average
[(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 point) of an adjustable low-pass 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.
video filter
A post-detection, low-pass filter that determines the bandwidth of the
video amplifier. It is used to average or smooth a trace. Refer also to
video bandwidth.
visual carrier
The visual carrier is the portion of a television signal that contains the
picture. A television signal contains both a visual and an aural carrier.
white level
The level of a visual carrier that corresponds to the maximum level of the
white area for a picture signal.
Glossary- 17