V - Volts. The SI unit of electrical potential difference. One volt is the difference in potential between two points of a conducting wire carrying a constant current of one ampere when the power dissipated between these two points is equal to one watt. It represents the energy available per unit charge within an electrical system (joules /coulombs).
V band - A band of frequencies between 46 and 56 gigahertz.
V.10 - A CCITT interface recommendation; electrical characteristics fo unbalanced double-current interchange circuits for use with integrated circuit equipment in the field of data communications. Electrically similar to RS-423.
V.11 - A CCITT interface recommendation; electrical characteristics for balanced double-current interchange circuits for use with integrated circuit equipment in the field of data communications. Electrically similar to RS-422.
V.20 - Parallel data transmission modems standardized for universal use in the general switched telephone network.
V.21 - A CCITT 300 bps dial modem recommendation for use in the general switched telephone network; similar to Bell 103.
V.22 bis - The worldwide standard for full-duplex 2-wire 2,400 bps modems (1,200 bps fall back), proposed by the CCITT and adopted by the telecommunications industry in 1984.
V.22 - A CCITT 1,200 bps full-duplex 2-wire modem standardized for use in the general switched telephone network; similar to Bell 212.
V.23 - A CCITT 5001 1,200 bps dial modem recommendation; similar to Bell 202.
V.24 - A CCITT interface recommendation that defines interchange circuits between data-terminal equipment and data circuit-terminating equipment; similar to and operationally -compatible with RS-232.
V.25 - A CCITT dial parallel interface recommendation.
V.25 bis - A CCITT dial serial interface recommendation.
V.25 ter - A CCITT 2,400 bps dial or 2-wire leased line modem recommendation.
V.26 - A CCITT 2,400/1,200 bps leased line modem recommendation; similar to Bell 201 B.
V.26 bis - A CCITT 2,400/1,200 bps dial line modem recommendation; similar to Bell 201 C.
V.27 - A CCITT 4,800 bps leased line modem recommendation with manual equalizer; similar to Bell 208 A.
V.27 bis - A CCITT 4,800/400 bps leased line modem recommendation with automatic equalizer.
V.27 ter - A CCITT 4,800 bps dial modem recommendation; similar to Bell 208 B.
V.28 - A CCITT interface recommendation that defines electrical characteristics for the interchange circuits defined by V.24; similar to and operationally compatible with RS- 232.
V.29 - A CCITT 9,600 bps leased line modem recommendation; similar to Bell 209.
V.32 - The worldwide standard for full-duplex 2-wire 9,600 bps modems (4,800 bps fall back), adopted in 1984. A V.32 modem must modulate signals at 9,600 by using QAM, it must transmit in full-duplex mode by using echo cancellation and it must be able to adjust its speed to match that of the answering modem.
V.35 CCITT high-speed modem cable assembly, 34/C - Terminated with an M series 34-pin connector. Used to interconnect controllers, PCs, etc. to high speed modems.
V.35 - Data transmission at 48 kbps using 60 to 108 kHz group band cir
V.42 - A worldwide standard for error detection in modems, adopted in 1984. Enables error-free data transfer at speeds up to 19,200 bps without the need for leased lines.cuits.
V.42 bis - A worldwide standard for data compression in modems, adopted in 1989.
VA - Volt-ampere. A designation of power in terms of volts and amperes. See APPARENT POWER.
VAR - A unit of reactive power that means volt-amperes, reactive.
VAR meter - An instrument used by power companies to measure the kVAR consumption. Utilities charge more for loads that consume large amount of reactive power.
VBR (variable bit rate) - One of the bit-rate modes available with MPEG compression. Will keep the image quality high even with increased motion but the bit rate will increase requiring,more bandwidth. Because of this, there is a need to insure that there is available bandwidth in the network to accommodate it.
VC - Varnished-cambric insulation.
VCSEL - Vertical-cavity surface-emitting laser is a type of semiconductor laser diode operating in the 850-nm wavelength window that is commonly used in Ethernet-based networks.
VDE - Association of German Electrical Engineers.
VELOCITY OF PROPAGATION - The transmission speed of an electrical signal down a length of cable compared to its speed in free space. Usually expressed as a percentage.
Vertical interval - The time of vertical retrace.
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.
VFD cable - Variable frequency drive cable. A power cable specially designed for use with VFDs. Usually has three-phase conductors, three symmetrically positioned grounding conductors and an overall RF shield. Also called adjustable speed drive (ASD) cable.
VG - Varnished-glass or nylon braid, 600 V or 3,000 V, 130°C.
VGA (video graphics array) - An evolving video graphics standard that increases the video display, resolution from the current 640-by-350 pixel resolution to up to 640-by-480 pixel resolution. For many applications the VGA improvement in resolution isnít required, but for CAD/CAM applications, this represents a significant improvement in resolution.
VHF - Very high frequency. The band extending from 30 to 300 MHz as designated by the Federal Communications Commission.
Video motion detection - A system that uses the video signal from a camera to determine if there is any movement in the picture and set of an alarm.
Video pair cable - A transmission cable containing low-loss pairs with an impedance of 125 ohms. Used for TV pickups, closed-circuit TV, telephone carrier circuits, etc.
Video type lens - An auto iris lens without an internal circuit to control the iris. All iris control voltages come from a circuit located within the camera.
Virtual Circuit - 1. Provision of a circuit-like service by the software protocols of a network, enabling two end points to communicate as though via a physical circuit. 2. A circuit, generally established on demand that permits communication between two points without a direct, dedicated link between them.
VISCA (video system control architecture) - A machine-control protocol designed by Sony to allow synchronized control of up to seven Visa devices on a daisy chain.
Viscosity - Internal friction or resistance to flow of a liquid: the constant ratio of shearing stress to rate of shear.
VLAN (virtual LAN or logical LAN) - A network of computers that behave as if they are connected to the same wire even though they may actually be physically located on different segments of a LAN. VLANs are configured through software rather than hardware, which make them extremely flexible.
VLF - Very low frequencies. The band extending from 10 to 30 kHz, as designated by the Federal Communications Commission.
VOD - Video on demand.
Voice frequency (VF) - Describes an analog signal within the range of transmitted speech, typically supported by an analog telecommunications circuit.
Voice PABX, voice-only PABX - A PABX for voice circuits; a telephone exchange.
Voice/data PABX - A device that combines the functions of a voice PABX and a data PABX, often with emphasis on the voice facilities.
Voice-grade channel, voice-grade line - A channel or line that offers the minimum bandwidth suitable for voice frequencies, usually 300 to 3,400 bps.
Volt - A unit of electrical “pressure.” One volt is the amount of electrical potential that will cause one ampere of current to flow through one ohm of resistance. Volt is a SI unit, the base units are joules (energy) per coulomb (charge) (J/C).
Voltage - Electrical potential or electromotive force expressed in volts.
Voltage breakdown - A test to determine the maximum voltage insulated wire can withstand before failure.
Voltage drop - The voltage developed across a conductor by the current and the resistance or impedance of the conductor. Also refers to the voltage used in a system to overcome the wiring resistance. Long runs of cable sized closely to the operating ampacity can suffer significant voltage drop that affects the load. Less than 5 percent is recommended by the NEC, around or less than 2 percent is ideal. Using larger conductor (less resistance) if possible will solve voltage drop problems.
Voltage rating - The highest voltage that may be continuously applied to a wire or cable in conformance with standards or specifications.
Voltage standing wave ratio (VSWR) - The ratio of the maximum effective voltage to the minimum effective voltage measured along the length of a mismatched radio frequency transmission line.
Voltage to ground - The voltage between an energized conductor and earth.
Voltage, cornoa extinction - The minimum voltage that sustains corona (partial discharge), determined by applying a corona producing voltage, then decreasing the voltage until corona is extinct.
Voltage, induced - A voltage produced in a conductor by a change in magnetic flux from an outside source.
Voltagedivider - A network consisting of impedance elements connected in series to which a voltage is applied and from which one or more voltages can be obtained across any portion of the network.
Volume resistivity - The resistance in ohms of a body of unit length and unit cross-sectional area.
VPN (virtual private network) - VPNs enable a customer to securely connect their offices using a protected ìtunnelî through a public infrastructure like the internet. They provide a more economical means to extend a corporate infrastructure and are an alternative to typical leased lines.
VSWR - See VOLTAGE STANDING WAVE RATIO.
VTL - Virtual tie line.
Vulcanization - A chemical reaction in which the physical properties of a polymer are changed by reacting it with cross-linking agents.
VW-1 - Vertical wire flame test. Formerly designated as FR1. A UL fire rating for single conductor cables. The test is described in UL Standard 1581.