AI-10
STANDING WAVE—The distribution of voltage and current formed by the incident and reflected
waves which have minimum and maximum points on a resultant wave that appears to stand still.
STANDING-WAVE RATIO (SWR)—The ratio of the maximum (voltage, current) to the minimum
(voltage, current) of a transmission line. Measures the perfection of the termination of the line.
STRATOSPHERE—Located between the troposphere and the ionosphere. Has little effect on radio
waves.
STUB—Short section of a transmission line used to match the impedance of a transmission line to an
antenna. Can also be used to produce desired phase relationships between connected elements of an
antenna.
SUDDEN IONOSPHERIC DISTURBANCE—An irregular ionospheric disturbance that can totally
blank out hf radio communications.
SUPERSONIC—Speed greater than the speed of sound.
SURFACE WAVE—A radio wave that travels along the contours of the earth, thereby being highly
attenuated.
TEMPERATURE INVERSION—The condition in which warm air is formed above a layer of cool air
that is near the earth's surface.
THREE-ELEMENT ARRAY—An array with two parasitic elements (reflector and director) and a
driven element.
TONES—Musical sounds.
TRANSLUCENT—A type of substance, such as frosted glass, through which some light rays can pass
but through which objects cannot be seen clearly.
TRANSMISSION LINE—A device designed to guide electrical energy from one point to another.
TRANSMITTING ANTENNA—The device used to send the transmitted signal energy into space.
TRANSPARENT—A type of substance, such as glass, that transmits almost all of the light waves that
fall upon it.
TRANSMISSION MEDIUMS—The various types of lines and waveguides used as transmission lines.
TRANSMITTER END—See INPUT END.
TRANSVERSE WAVE MOTION—The up and down motion of a wave as the wave moves outward.
TROPOSPHERE—The portion of the atmosphere closest to the earth's surface, where all weather
phenomena take place.
TROPOSPHERIC SCATTER—The propagation of radio waves in the troposphere by means of scatter.
TROUGH (BOTTOM)—The peak of the negative alternation (maximum value below the line).
TUNED LINE—Another name for the resonant line. This line uses tuning devices to eliminate the
reactance and to transfer maximum power from the source to the line.
