(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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