admittance Symbol, Y. Unit, siemens (formerly mho). The property denoting the comparative ease with which an alternating current flows through a circuit or device. Admittance is the reciprocal of impedance (Z ): Y = 1/Z. adp 1. Abbreviation of AMMONIUM DIHYDROGEN PHOSPHATE, a piezoelectric compound used for sonar crystals. 2. Abbreviation of AUTOMATIC DATA PROCESSING. adsorption Adhesion of a thin layer of molecules of one substance to the surface of another without absorption. An example is adsorption of water to the surface of a dielectric. This term is often confused with ABSORPTION because the spellings of the two words are almost identical. Compare ABSORPTION | 16 admittance affirmative admittance Symbol Y. Unit siemens formerly mho . The property denoting the comparative ease with which an alternating current flows through a circuit or device. Admittance is the reciprocal of impedance Z Y 1 Z. adp 1. Abbreviation of AMMONIUM DIHYDROGEN PHOSPHATE a piezoelectric compound used for sonar crystals. 2. Abbreviation of AUTOMATIC DATA PROCESSING. adsorption Adhesion of a thin layer of molecules of one substance to the surface of another without absorption. An example is adsorption of water to the surface of a dielectric. This term is often confused with ABSORPTION because the spellings of the two words are almost identical. Compare ABSORPTION. adu Abbreviation of automatic dialing unit. advanced-class license An amateur-radio license conveying all operating privileges except for a few small bands that are allocated to extra-class licensees. The second-highest class of amateur license. advance information Data published prior to the actual production or availability of a manufactured component circuit or system. Advance information is often only an approximate reflection of the expected characteristics of a device. advance wire A resistance wire used in thermocouples and precision applications. It is an alloy of copper and nickel which has high resistivity and a negligible temperature coefficient of resistance. aeolight A glow lamp using a cold cathode and a mixture of inert gases. Because its illumination can be regulated with an applied signal voltage it is sometimes used as a modulation indicator for motion-picture sound recording. aerial See ANTENNA. aerial cable A wire or cable run through the air using support structures such as towers or poles. aerodiscone antenna A miniature discone antenna designed for use on aircraft. aerodynamics The science dealing with forces exerted by air and other gases in motion especially upon bodies such as aircraft moving through these gases. aerogram See RADIOGRAM. aeromagnetic Pertaining to
