CCTV Glossary
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T1. - A digital transmission link with a capacity of 1.544 Mbps. T1 uses two pairs of normal twisted
wires. T1 lines are used for connecting networks across remote distances. Bridges and routers are
used to connect LANs overT1 networks.
T1 channels. - In North America, a digital transmission channel carrying data at a rate of 1.544
million bits per second. In Europe, a digital transmission channel carrying data at a rate of 2.048
million bits per second. AT&T term for a digital carrier facility used to transmit a DS-1 formatted
digital signal at 1.544 Mbps.
T3 channels. - In North America, a digital channel that communicates at 45.304 Mbps commonly
referred to by its service designation of DS-3.
TBC. - Time base correction. Synchronization of various signals inside a device such as a
multiplexer or a time base corrector.
TDG. - Time and date generator.
TDM. - Time division multiplex. A time-sharing of a transmission channel by assigning each user a
dedicated segment of each transmission cycle.
Tearing. - A lateral displacement of the video lines due to sync instability. It appears as though
parts of the images have been torn away.
Teleconferencing. - Electronically linked meeting conducted among groups in separate
geographic locations.
Telemetry. - Remote controlling system of, usually, digital encoded data, intended to control pan,
tilt, zoom, focus, preset positions, wash, wipe and similar. Being digital, it is usually sent via twisted
pair cable or coaxial cable together with the video signal.
Termination. - This usually refers to the physical act of terminating a cable with a special
connector, which for coaxial cable is usually BNC. For fiber optic cable this is the ST connector. It
can also refer to the impedance matching when electrical transmission is in use. This is especially
important for high frequency signals, such as the video signal, where the characteristic impedance
is accepted to be 75-W.
TFT. Thin-film-transistor. - This technology is used mainly for manufacturing flat computer and
video screens that are superior to the classic LCD screens. Color quality, fast response time and
resolution are excellent for video.
Time lapse VCR (TL VCR). - A video recorder, most often in VHS format, that can prolong the
video recording on a single tape up to 960 hours (this refers to a 180 min tape). This type of VCR is
often used in CCTV systems. The principle of operation is very simple – instead of having the
video tape travel at a constant speed of 2.275 cm/s (which is the case with the domestic models of
VHS VCRs), it moves with discrete steps that can be controlled. Time Lapse VCRs have a number
of other special functions very useful in CCTV, such as external alarm trigger, time and date
superimposed on the video signal, alarm search and so on.
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