CCTV Glossary
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V
Variable bit rate. - Operation where the bit rate varies with time during the decoding of a
compressed bit stream.
VDA. - See video distribution amplifier.
Vectorscope .- An instrument similar to an oscilloscope, that is used to check and/or align
amplitude and phase of the three color signals (RGB).
Velocity of propagation.- Speed of signal transmission. In free space, electromagnetic waves
travel at the speed of light. In coaxial cables, this speed is reduced by the dielectric material.
Commonly expressed as percentage of the speed in free space.
Vertical interval. - The portion of the video signal that occurs between the end of one field and the
beginning of the next. During this time, the electron beams in the monitors are turned off (invisible)
so that they can return from the bottom of the screen to the top to begin another scan.
Vertical interval switcher. - A sequential or matrix switcher that switches from one camera to
another exactly in the vertical interval, thus producing roll-free switching. This is possible only if the
various camera sources are synchronized.
Vertical resolution. - Chrominance and luminance detail expressed vertically in the picture tube.
Limited by the number of scan lines.
Vertical retrace. - The return of the electron beam to the top of a television picture tube screen or
a camera pickup device target at the completion of the field scan.
Vertical shift register. - The mechanism in CCD technology whereby charge is read out from the
photosensors of an interline transfer or frame interline transfer sensor.
Vertical sync pulse. - A portion of the vertical blanking interval which is made up of blanking level.
Synchronizes vertical scan of television receiver to composite video signal. Starts each frame at
same vertical position.
Vestigial sideband transmission. - A system of transmission wherein the sideband on one side of
the carrier is transmitted only in part.
VGA. - Video graphics array.
Video bandwidth. - The highest signal frequency that a specific video signal can reach. The
higher the video bandwidth, the better the quality of the picture. A video recorder that can produce
a very broad video bandwidth generates a very detailed, high quality picture on the screen. Video
bandwidths used in studio work vary between 3 and 12 MHz.
Video distribution amplifier (VDA). - A special amplifier for strengthening the video signal so that
it can be supplied to a number of video monitors at the same time.
Video gain. - The range of light-to-dark values of the image that are proportional to the voltage
difference between the black and white voltage levels of the video signal. Expressed on the
waveform monitor by the voltage level of the whitest whites in the active picture signal. Video gain
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