CCTV Glossary
Cascadia Video Products LLC
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Back-focus - A procedure of adjusting the physical position of the CCD-chip/lens to achieve the
correct focus for all focal length settings (especially critical with zoom lenses).
Back porch - 1. The portion of a video signal that occurs during blanking from the end of
horizontal sync to the beginning of active video. 2. The blanking signal portion that lies between
the trailing edge of a horizontal sync pulse and the trailing edge of the corresponding blanking
pulse. Color burst is located on the back porch.
Balanced signal - In CCTV this refers to a type of video signal transmission through a twisted pair
cable. It is called balanced because the signal travels through both wires, thus being equally
exposed to the external interference, so by the time the signal gets to the receiving end, the noise
will be cancelled out at the input of a differential buffer stage.
Balun - This is a device used to match or transform an unbalanced coaxial cable to a balanced
twisted pair system.
Bandwidth - The complete range of frequencies over which a circuit or electronic system can
function with minimal signal loss, usually measured to the point of less than 3 dB. In PAL systems
the bandwidth limits the maximum visible frequency to 5.5 MHz, in NTSC to 4.2 MHz. The ITU
601 luminance channel sampling frequency of 13.5 MHz was chosen to permit faithful digital
representation of the PAL and NTSC luminance bandwidths without aliasing.
Baseband - The frequency band occupied by the aggregate of the signals used to modulate a
carrier before they combine with the carrier in the modulation process. In CCTV the majority of
signals are in the baseband.
Baud - Data rate, named after Maurice Emile Baud, which generally is equal to 1 bit/s. Baud is
equivalent to bits per second in cases where each signal event represents exactly 1 bit. Typically,
the baud settings of two devices must match if the devices are to communicate with one another.
BER - Bit error rate. The ratio of received bits that are in error relative to the total number of bits
received, used as a measure of noise induced distortion in a digital bit stream. BER is expressed
as a power of 10. For example, a 1 bit error in 1 million bits is a BER of 10–6.
Betamax - Sony’s domestic video recording format, a competitor of VHS.
Bias - Current or voltage applied to a circuit to set a reference operating level for proper circuit
performance, such as the high frequency bias current applied to an audio recording head to
improve linear performance and reduce distortion.
Binary - A base 2 numbering system using the two digits 0 and 1 (as opposed to ten digits [0-9] in
the decimal system). In computer systems, the binary digits are represented by two different
voltages or currents, one corresponding to zero and another corresponding to one. All computer
programs are executed in binary form.
Bipolar - A signal containing both positive-going and negative-going amplitude. May also contain
a zero amplitude state.
(8 Seiten)
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