value engineering - An effort to examine and weigh the initial cost; evaluate the maintenance expense and ultimate worth of certain materials, components, and systems; and assess performance at the lowest price consistent with the project criteria during the design development/ preliminary design phase.

valve-regulated lead-acid (VRLA) cell - A battery cell that is regulated by a pressure relief valve and does not allow for the adding of water. Also called sealed or maintenance-free cells.

vampire tap - A device used to provide an electrical connection to a transceiver into thick Ethernet cable without breaking/cutting the cable.

variable air volume (VAV) - A self-contained heating, ventilating, and air-conditioning (HVAC) unit that uses a built-in microprocessor-based controller to control environmental air to a specific zone via a damper. The unit is placed near the end of a HVAC duct and can also monitor temperature inputs from local sensors.

varistor - An electrical component whose resistance depends on the applied voltage or current.

vault - A telecommunications space, typically subterranean, located within or between buildings and used for the distribution, splicing, and termination of cabling. These spaces may be established as a maintenance hole in campus environments or they may include active equipment in addition to passive cabling such as in a controlled environment vault.

velocity of propagation - The speed of transmission along a cable relative to the speed of light in a vacuum.

ventilated channel - Channel section with a one-piece bottom no more than 150 mm (6.0 in) wide.

ventilated trough - A ventilated bottom with side rails.

vertical down lead (VDL) - A ground wire placed on a pole that leads down to the ground electrode at the base of the pole.

vertical spiral - An omnidirectional vertical log-periodic antenna may be formed using a continuous spiral with the radius and spacing of each turn varying in the same manner as the dipole array relationship. Such an antenna must be operated over a ground plane and fed unbalanced.

very high frequency (VHF) - Frequencies from 30 MHz to 300 MHz.

very low frequency (VLF) - Frequencies from 3 kHz to 30 kHz.

V-groove - Position in fusion splicer where optical fiber strand is placed.

vibration resistance - The ability of an antenna to mechanically survive the flexing and vibration caused by wind blowing across it and its supporting structure.

vibration spacer - A material placed between conduits and support iron used to cushion a conduit run attached to bridges from the vibrational stress associated with moving traffic loads on the bridge structure.

Vigants formula - 1. An equation that models performance factors used when providing space diversity to an unprotected system. 2. An equation that models rain outages of radio frequency systems.

vignetting - A tunnel or porthole image that is produced by using a smaller image-size format lens on a larger image-size format camera (i.e., 8.3 mm lens and 13 mm camera). Similar to an unbordered picture, often a portrait, that shades off into the surrounding color at the edges. Conversely, one can use a larger image-size lens on a smaller image-size format camera.

virtual circuit (VC) - A communications path through an internetwork that appears to be a dedicated circuit between two network devices.

virtual LAN (VLAN) - A technique made possible by switching technologies that permits the logical grouping of any number of network devices into one or more subnetworks to improve traffic management and/or security.

virtual private network (VPN) - A combination of hardware and software technologies designed to enable secure passage of organizational network traffic over the Internet. See also tunnel.

virtualization - The software and procedures that make it possible for users and administrators to view and manage a group of storage devices as a single unit regardless of differences in capacities, locations, and device types.

visible light - The frequency range of light that is detectible by the human eye. The frequency (wavelength) range is from 390 nm to 780 rim.

visual fault locator (VFL) - Small handheld visible light source consisting of a light emitting diode, lamp, or visible laser. Used to identify optical fibers, faulty connectors, or optical fiber breaks. See hot red light.

voice band - An analog voice circuit that transmits signals in a frequency band of 300-3400 Hz.

voice frequency (VF) - Pertaining to those frequencies within the part of the audio range that is used for the transmission of speech.

voice grade (VG) - AnyLAN A hub-based LAN using demand priority access method technology (IEEE 802.12) that can transport token ring or Ethernet frames at a transfer rate of 100 Mb/s.

voice over Internet prbtocol (VoIP) - A system in which voice signals are converted to packets and transmitted over a network using Transmission Control Protocol/Internet Protocol.

voice recognition - Identifying an individual by comparing previously stored voice recordings key words or phrases with the same key phrases spoken at the same time access is requested.

volt (V) - A unit of electromotive force or potential difference that will cause a current of one ampere to flow through a resistance of one ohm.

voltage - Electrical potential or potential difference expressed in volts.

voltage gradient - The change in voltage differential per unit distance. See also electric field strength.

voltage standing wave ratio (VSWR) - The ratio of the maximum to the minimum voltage in the standing wave pattern that appears along a transmission line.

voltage standing wave ratio (VSWR) protection - A device that measures the level of undesirable reverse power caused by impedance mismatches between a radio frequency (RF) transmitter, its transmission line, and the antenna. The measuring and limiting reverse RF power will prevent damage of these components.

volt-ohmmeter (VOM) - An instrument used to measure electrical characteristics. See multimeter.

volume control - A device used to increase and decrease the audio level of a speaker(s).