18WuD2x

Trinitron • tropospheric propagation 695
this tube. The gun has three cathodes that modulate
the three color beams (red, green, and blue).
The beams are accelerated by common grids and
are focused at different angles by convergence
plates.
Trinoscope See TRINITRON.
triode A three-electrode tube or transistor, embodying
an anode, cathode, and a control electrode
as the principal elements.
triple-diffused transistor A diffused transistor in
which the base and emitter are diffused into the
top face of the chip, and the collector into the bottom
face.
triple diode An assembly of three (often closely
matched) semiconductor diodes in a single
housing.
tripler
1. A rectifier that delivers a direct-current
output voltage at approximately triple the peak
value of the alternating-current input voltage.
2. An amplifier or other circuit that delivers an
output signal at triple the frequency of the input
signal.
triplexer In radar, a device that facilitates the use
of two receivers at the same time.
R1 C2 CR3 +
CR1
ac
CR2
in E rms C3
+
C1
tripler, 1
Tri-state logic Digital logic in which there are
three possible states, rather than the usual two.
The conditions are defined as 0, 1, and undecided.
Trade name of National Semiconductor.
tritium Symbol, T or H 3 . An isotope of hydrogen
whose nucleus contains two neutrons and one
proton. Compare DEUTERIUM.
TRL Abbreviation of transistor-resistor logic (see
RESISTOR-TRANSISTOR LOGIC).
Trojan horse A program written with the malicious
intent of sabotaging the operating system and/or
files in a computer. It is somewhat similar to a
VIRUS; it is occasionally spread via software
whose origin is questionable or unknown.
troposcatter See TROPOSPHERIC-SCATTER
PROPAGATION.
troposphere The portion of the atmosphere in
which virtually all weather phenomena occur. It
extends from the surface to an altitude of 8 to 12
miles above sea level.
+
+
−
tropospheric bending A common type of radiowave
propagation that takes place when radio
waves are refracted in the lower atmosphere.
This effect is most dramatic near weather fronts,
where warm, relatively light air lies above cool,
heavy air. The cooler air has a higher index of refraction
than the warm air, causing radiofrequency
electromagnetic fields to be bent
downward at a considerable distance from the
transmitter. It is often responsible for anomalies
in reception of FM and TV broadcast signals.
Compare TROPOSPHERIC DUCTING, TROPO-
SPHERIC-SCATTER PROPAGATION.
tropospheric ducting Also called duct effect. A
form of tropospheric propagation that occurs
close to the earth’s surface at very-high
frequencies (VHF) and ultra-high frequencies
(UHF). A duct forms when a layer of cool air
becomes sandwiched between two layers of
warmer air. Total internal reflection of the
electromagnetic (EM) field takes place inside
the duct. For this phenomenon to provide
communications, both the transmitting and
receiving antennas must be located within the
same duct, and this duct must be unbroken and
unobstructed between the two locations. A duct
might measure only a few feet from top to bottom,
but cover thousands of square miles
parallel to the surface. Compare TROPO-
SPHERIC BENDING, TROPOSPHERIC-SCATTER
PROPAGATION.
tropospheric propagation Also called tropo. Overthe-horizon
propagation of radio-frequency electromagnetic
waves that occurs as a result of
reflection, scattering, and/or refraction in the
troposphere, the lowest 10 or 12 miles of the
earth’s atmosphere. At wavelengths shorter than
about 15 m (frequencies above 20 MHz), refraction
and reflection can take place within and between
air masses of different density. The air also
produces some scattering of EM energy at
wavelengths shorter than about 3 m (frequencies
above 100 MHz). “Tropo” can often allow