18WuD2x

322 ground-mounted vertical antenna • groundtrack
The center conductor of the cable is connected to
the base of the radiator, and the shield is connected
to a ground system. Radial wires, usually
buried just below the surface, minimize losses.
The antenna can be made resonant on several
frequencies by inserting multiple loading coils or
traps in the radiator. The chief advantages of this
antenna are unobtrusiveness and ease of installation.
The main problems are marginal efficiency
and susceptibility to human-made electromagnetic
noise. See also RADIAL, 1. Compare
GROUND-PLANE ANTENNA.
ground noise 1. Electrical noise that results from
a faulty ground connection. 2. Background noise.
3. In wire circuits, such as a telephone system,
electrical noise that results from fluctuations in
ground current.
ground plane 1. A metal plate or a system of horizontal
rods or wires mounted high on a mast, at
the base of a vertical antenna, to provide a radiofrequency
ground at a point several wavelengths
above the surface of the earth. Also see GROUND-
PLANE ANTENNA. 2. In noise and interference
tests, a sheet metal structure used to simulate
the skin of an aircraft or missile. 3. On a circuit
board, a thin metallic sheet, usually bound to the
underside, that serves as a common ground and
RF shield.
ground-plane antenna A vertical radiator operated
against a system of quarter-wave radials,
elevated at least a quarter wavelength above the
earth’s surface and fed with coaxial cable.
The center conductor of the cable is connected
to the base of the radiator, and the shield is connected
to three or four quarter-wave radials that
run outward from the base of the radiator. At
shorter wavelengths, a disk or cone can replace
the radials. The chief advantages of this antenna
are simplicity and high efficiency. The
main problem is susceptibility to human-made
electromagnetic noise. See also RADIAL,
1. Compare GROUND-MOUNTED VERTICAL
ANTENNA.
ground plate A metal plate buried in the earth to
provide a low-resistance ground connection.
ground-position indicator Abbreviation, GPI. A
computer system that gives a continuous indication
of an aircraft’s position in terms of heading,
elapsed time, and speed, with respect to the surface.
This provides a more useful indication of the
aircraft position than an air-speed indicator because
it is not affected by high-altitude winds.
ground potential See ZERO POTENTIAL, 3.
ground protection The use of a GROUND-FAULT
INTERRUPTER.
ground-reflected wave A radio wave component
that results from ground reflection.
ground reflection The reflection of a radio wave by
the earth.
ground resistance The direct-current resistance of
a connection to the earth, or the resistance between
two points through the earth. The magnitude
of the resistance depends on several factors:
composition of the soil, amount of moisture, soil
electrolytic action, and the area of contact with
the earth.
ground return 1. The point or path used to return
a circuit to ground for completion. 2. In radar,
echoes returned from the earth’s surface (including
reflections from objects on it).
ground-return circuit A circuit, such as a singlewire
telephone line, in which earth ground forms
one leg of the circuit. Compare METALLIC CIR-
CUIT.
ground rod A strong metal rod driven deep into the
earth as a point of ground connection.
ground speed The speed of an aircraft or missile,
relative to the surface of the earth.
ground state The least-energy level of all possible
states in a system.
ground support equipment Electronic surfacebased
apparatus upon which the functioning of a
weapons system is dependent.
ground switch A switch for grounding an outside
antenna during idle periods. Also called lightning
switch. Ideally, antennas should be disconnected
from equipment, as well as grounded, when not
in use.
ground-to-air communication Radio or radar
transmission from a land station to an aircraft in
flight.
ground-to-ground 1. Pertaining to communications
between land-based stations. 2. Pertaining
to missiles intended for use between points on
the surface of the earth.
ground-to-ground communication Communications
between land-based stations.
groundtrack For an earth-orbiting satellite, the
path followed by the point on the earth’s surface
from which the spacecraft appears directly overhead.
For most satellites, this path shifts toward
the west for each succeeding orbit, because the
earth rotates eastward underneath the satellite.
For geostationary satellites, the point never