AI-11
TURNSTILE ANTENNA—A type of antenna used in vhf communications that is omnidirectional and
consists of two horizontal half-wave antennas mounted at right angles to each other in the same
horizontal plane.
TWISTED PAIR—A line consisting of two insulated wires twisted together to form a flexible line
without the use of spacers.
TWO-WIRE OPEN LINE—A parallel line consisting of two wires that are generally spaced from 2 to 6
inches apart by insulating spacers.
TWO-WIRE RIBBON (TWIN LEAD)—A parallel line similar to a two-wire open line except that
uniform spacing is assured by embedding the two wires in a low-loss dielectric.
ULTRASONIC—Sounds above 20,000 hertz.
UNIDIRECTIONAL ARRAY—An array that radiates in only one general direction.
UNTUNED LINE—Another name for the flat or nonresonant line.
V ANTENNA—A bi-directional antenna, shaped like a V, which is widely used for communications.
VELOCITY—The rate at which a disturbance travels through a medium.
VERTICAL AXIS—On a graph, the straight line axis oriented from bottom to top.
VERTICAL PATTERN—The part of a radiation pattern that is radiated in the vertical plane.
VERTICALLY POLARIZED—Waves radiated with the E field component perpendicular to the earth's
surface.
VOLTAGE-FEED METHOD—Same as END FEED METHOD.
VOLTAGE STANDING-WAVE RATIO (VSWR)—The ratio of maximum to minimum voltage of a
transmission line.
WAVE ANTENNA—Same as BEVERAGE ANTENNA.
WAVE MOTION—A recurring disturbance advancing through space with or without the use of a
physical medium.
WAVE TRAIN—A continuous series of waves with the same amplitude and wavelength.
WAVEFRONT—A small section of an expanding sphere of electromagnetic radiation, perpendicular to
the direction of travel of the energy.
WAVEGUIDE—A hollow metal tube used as a transmission line to guide energy from one point to
another.
WAVELENGTH—(1) The distance in space occupied by 1 cycle of a radio wave at any given instant.
(2) The distance a disturbance travels during one period of vibration.
YAGI ANTENNA—A multielement parasitic array. Elements lie in the same plane as those of the end-
fire array.
