Fiber Optic Glossary: U, V

UHF: Abbreviation for ultra high frequency. The frequencies, ranging from 300 MHz to 3000 MHz, in the electromagnetic spectrum. Contains off-air television channels 21-68.
UL: Abbreviation for Underwriter’s Laboratory. An organization that tests product safety for a wide variety of products. UL approved products carry the symbol shown at right.
Unidirectional: Operating in one direction only.
Unity Gain: A concept in which all the amplifiers in a cascade are in balance with their power inputs and outputs. Unity gain can be achieved by adjusting the receiver output, either by padding or attenuation in the node, to the proper level determined by the RF input.
UTP cabling (Unshielded Twisted Pair):
UV: Abbreviation for ultraviolet. That portion of the electromagnetic spectrum in which the longest wavelength is just below the visible spectrum, extending from approximately 4 nm to 400 nm.

V: Abbreviation for Volt. A unit of electrical force or potential, equal to the force that will cause a current of one Amp to flow through a conductor with a resistance of one Ohm.
V_AC: Abbreviation for Volts, AC. Voltage using alternating current.
VCSEL: See vertical cavity surface-emitting laser.
V_DC: Abbreviation for Volts, DC. Voltage using direct current.
VDSL: Abbreviation for very high data rate digital subscriber line. A DSL operating at a data rate higher than that of HDSL. See also DSL.
Vector Quantization (VQ): A digital video compression technique based on Shannon’s distortion-rate theory which states that the performance of data compression systems improves if blocks of data are coded, with larger coded data blocks giving better performance.
Vertical Cavity Surface-emitting Laser: Lasers that emit light perpendicular to the plane of the wafer they are grown on. They have very small dimensions compared to conventional lasers and are very efficient.
Vestigial-sideband (VSB) Transmission: A modified double-sideband transmission in which one sideband, the carrier, and only a portion of the other sideband are transmitted. See also sideband.
VGA: Abbreviation for video graphics array. A high-resolution color standard for computer monitors.
VHF: Abbreviation for very high frequency. The frequencies, ranging from 30 MHz to 300 MHz, in the electromagnetic spectrum. Contains off-air television channels 2-12.
Video on Demand (VOD): A term used for interactive or customized video delivery service.
Videoconferencing: Conducting conferences via a video telecommunications system.
Videophone: A telephone-like service with a picture as well as sound.
Virtual Circuit (VC): A communications arrangement in which data from a source user may be passed to a destination user over various real circuit configurations during a single period of communication, usually on a per call basis, although permanent connections can be established.
Visible Light: Electromagnetic radiation visible to the human eye; wavelengths of 400-700 nm.
VOD: See video on demand.
Voice Circuit: A circuit capable of carrying one telephone conversation or its equivalent; the standard sub-unit in which telecommunication capacity is counted. The U.S. analog equivalent is 4 kHz. The digital equivalent is 64 kbit/s in North America and in Europe.
VPN: Abbreviation for virtual private network. A protected information-system link utilizing tunneling, security controls, and end-point address translation giving the end user the impression that a dedicated line exists between nodes.
VSB: See vestigial-sideband transmission.