AI-5
HORIZONTALLY POLARIZED—Waves that are radiated with their E field component parallel to the
Earth's surface.
INCIDENT WAVE—(1) The wave that strikes the surface of a medium. (2) The wave that travels from
the sending end to the receiving end of a transmission line.
INDUCTION FIELD—The electromagnetic field produced about an antenna when current and voltage
are present on the same antenna.
INDUCTION LOSSES—The losses that occur when the electromagnetic field around a conductor cuts
through a nearby metallic object and induces a current into that object.
INFRASONIC (SUBSONIC)—Sounds below 15 hertz.
INPUT END—The end of a two-wire transmission line that is connected to a source.
INPUT IMPEDANCE—The impedance presented to the transmitter by the transmission line and its
load.
INTENSITY (OF SOUND)—The measurement of the amplitude of sound energy. Sometimes
mistakenly called loudness.
INTERCEPT—The point where two lines drawn on a graph cross each other.
INTERFERENCE—Any disturbance that produces an undesirable response or degrades a wave.
IONOSPHERE—The most important region of the atmosphere extending from 31 miles to 250 miles
above the earth. Contains four cloud-like layers that affect radio waves.
IONOSPHERIC STORMS—Disturbances in the earth's magnetic field that make communications
practical only at lower frequencies.
IONIZATION—The process of upsetting electrical neutrality.
ISOTROPIC RADIATION—The radiation of energy equally in all directions.
LEAKAGE CURRENT—The small amount of current that flows between the conductors of a
transmission line through the dielectric.
LIGHT RAYS—Straight lines that represent light waves emitting from a source.
LOAD END—See OUTPUT END.
LOADING—See LUMPED-IMPEDANCE TUNING.
LOBE—An area of a radiation pattern plotted on a polar-coordinate graph that represents maximum
radiation.
LONG-WIRE ANTENNA—An antenna that is a wavelength or more long at its operating frequency.
LONGITUDINAL WAVES—Waves in which the disturbance (back and forth motion) takes place in
the direction of propagation. Sometimes called compression waves.
LOOP—The curves of a standing wave or antenna that represent amplitude of current or voltage.
