A
Glossary a and b
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AGC: Automatic gain control – electronic circuitry to increase
the video signal in low light conditions. This usually introduces ‘noise’ in the picture giving a grainy appearance. Camera
specifications must always be considered with AGC off. |
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| ANALOGUE SIGNAL:
In video, the representation of a
camera scene by varying voltages in the video signal, the voltage being directly proportional to the light level. |
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| APERTURE:
The light gathering area of a lens. The iris
controls the size of the aperture. |
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| ARMOUR:
Extra protection for a cable that improves resistance to cutting and crushing. The most common material used is steel. |
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| ATTENUATION:
A term that refers to signal loss in a transmission system. |
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| AUTOMATIC IRIS:
A lens that automatically adjusts to allow
the correct amount of light to fall on the imaging device. There is a tiny motor and amplifier built in which generally receives a
control signal from the camera to maintain a constant one volt peak to peak (pp) video level. There are two manual controls on
the lens to allow compensation for varying conditions of ‘peak’ and ‘average’ light. |
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| BACK FOCUS:
A mechanical adjustment in a camera that moves the imaging device relative to the lens to compensate for
different back focal lengths of lenses. An important adjustment
when a zoom lens is fitted. |
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| BALANCED SIGNAL:
A video signal converted to a balanced
signal, usually to enable it to be transmitted along a ‘twisted pair’ cable. Used in situations where the cabling distance is too
great and which would produce unacceptable losses in a coaxial cable. |
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| BALUN:
A transformer that levels out impedance differences so that a signal generated on to a coaxial cable can transfer on to a twisted pair. |
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| BANDWIDTH:
The range of frequencies a transmission line or
channel can carry: the greater the bandwidth, the greater the information-carrying
capacity of a channel. For a digital channel
this is defined in bit/s. |
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| BITS PER SECOND:
The rate at which individual bits are transmitted across a communications link or circuit; written
bit/s. One thousand bit/s is 1 Kbit/s, and one million bit/s is 1 Mbit/s. |
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(Top)
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