(3) ELECTROMAGNETIC. The entire range of electromagnetic waves arranged in order of their frequencies.
SPORADIC E LAYER—Irregular cloud-like patches of unusually high ionization. Often forms at heights near the normal E-layer.
SPREADER—Insulator used with transmission lines and antennas to keep the parallel wires separated.
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 to the minimum amplitudes of corresponding components of a field, voltage, or current along a transmission line or waveguide in the direction of propagation measured at a given frequency. 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.
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.
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.
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.
TRANSVERSE ELECTRIC MODE—The entire electric field in a waveguide is perpendicular to the wide dimension and the magnetic field is parallel to the length. Also called the TE mode.
TRANSVERSE MAGNETIC MODE—The entire magnetic field in a waveguide is perpendicular to the wide dimension ("a" wall) and some portion of the electric field is parallel to the length. Also called the TM mode.
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.
TURNSTILE ANTENNA—A type of antenna used in vhf communications that is omnidirectional
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