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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. Time lapse video recording. The intermittent recording of video signals at intervals to extend the recording time of the recording medium. It is usually measured in reference to a 3-hr (180-min) tape. Time multiplexing. The technique of recording several cameras onto one time lapse VCR by sequentially sending camera pictures with a timed interval delay to match the time lapse mode selected on the recorder. T-pulse to bar. A term relating to frequency response of video equipment. A video signal containing equal amplitude T-pulse and bar portions is passed through the equipment and the relative amplitudes of the T-pulse and bar are measured at the output. A loss of response is indicated when one portion of the signal is lower in amplitude than the other. Tracking. The angle and speed at which the tape passes the video heads. Transcoder. A device that converts one form of encoded video to another, e.g., to convert NTSC video to PAL. Sometimes mistakenly used to mean translator. Transducer. A device that converts one form of energy into another. For example, in fiber optics, a device that converts light signals into electrical signals. Translator. A device used to convert one component set to another, e.g., to convert Y, R-Y, B-Y signals to RGB signals. Transponder. The electronics of a satellite that receives an uplinked signal from the earth, amplifies it, converts it to a different frequency and returns it to the earth. TTL. 1. Transistor-transistor logic. A term used in digital electronics mainly to describe the ability of a device or circuit to be connected directly to the input or output of digital equipment. Such compatibility eliminates the need for interfacing circuitry. TTL signals are usually limited to two states, low and high, and are thus much more limited than analog signals. 2. Thru-the-lens viewing or color measuring. Twisted-pair. A cable composed of two small insulated conductors twisted together. Since both wires have nearly equal exposure to any interference, the differential noise is slight. UHF signal. Ultra high frequency signal. In television it is defined to belong in the radio spectrum between 470 MHz and 850 MHz. Unbalanced signal. In CCTV, this refers to a type of video signal transmission through a coaxial cable. It is called unbalanced because the signal travels through the center core only, while the cable shield is used for equating the two voltage potentials between the coaxial cable ends. Underscan. Decreases raster size H and V so that all four edges of the picture are visible on the monitor. UPS. Uninterruptible power supply. These are power supplies used in the majority of high security systems, whose purpose is to back-up the system for at least 10 minutes without mains power. The duration of this depends on the size of the UPS, usually expressed in VA, and the current consumption of the system itself. UTP. Unshielded twisted pair. A cable medium with one or more pairs of twisted insulated copper conductors bound in a single sheath. Now the most common method of bringing telephone and data to the desktop. |