Installation guide

GLOSSARY
40
GLOSSARY OF ANTENNA
SYSTEM TERMS
Acrylic Insulator–A plastic material that is used to
weatherproof outdoor antenna system connections.
It is applied in liquid form, typically by aerosol can.
Alignment Bearing (rotor)–A ball bearing-equipped
guy ring that is slipped onto the antenna mast above
the rotor to permit guying of the mast section rotated
by the rotor.
Antenna Discharge Unit (Lightning Arrestor)–A
small device that is inserted into the transmission
line and connected to a grounding wire or strap to
discharge static electricity to ground before it can
enter and damage a TV receiver.
Array, Multiple–See Multiple Array.
Attenuation–A decrease in the strength (level) of a
signal as it is transmitted or carried by wire(s) from
one point to another. In antenna systems, attenuation
is usually an undesirable characteristic.
Balun (matching transformer)–A small device
that matches the impedance of one component,
transmission line, or circuit to that of another to
prevent loss of signal strength and other unwanted
characteristics. In antenna systems, baluns typically
are used to match 75 ohm coaxial cable to the
300 ohm output of an antenna or the 300 ohm input of
a TV.
Band, Low (TV)–See Low Band.
Band, High (TV)–See High Band.
Beamwidth–The angle formed by the two compass
directions that outline the boundaries of the area
from which the front of an antenna can intercept
signals and deliver them to the output at relatively
equal levels. Generally, the narrower the beamwidth
of an antenna, the greater the directivity and gain.
Boot, Weather–See Weather Boot.
Brown Goods–A wide variety of consumer electronic
products that traditionally have brown or darker
cabinets than home appliances such as refrigerators,
washers and dryers. Examples of brown goods are TV
receivers and radios.
Carrier, Picture (TV)–See Picture Carrier.
Carrier, Sound (TV)–See Sound Carrier.
Coaxial Cable (coax)–A type of round transmission
line composed of a central conductor (wire)
surrounded in turn by an insulating material
(dielectric), and a metallic shielding material which
typically is braided and acts as the second conductor.
(Some types of coaxial cable have an aluminum foil
shield under which is run a separate wire strand that
serves as the second conductor.) These elements, in
turn, are covered by a thin layer of insulating and
weatherproofing material such as polyvinyl. Coaxial
cables used as home TV transmission lines have an
impedance of 75 ohms.
Decibel (dB)–A measurement term that describes the
strength (level) of a signal in logarithmic relation to a
reference strength (level). For example, when the
signal strength is expressed in micro-volts, an
increase of the signal strength by 6 dB means that the
signal strength has been doubled.
Dielectric–An insulating material placed between
conductors to prevent the conductors from physically
contacting one another (shorting out). In coaxial
cable, insulating material surrounds the central con-
ductor to prevent it from touching the metallic shield
(and other conductor wire if one is used.) The insu-
lating material also maintains a specific amount of
space between the central conductor and the other
conductor. This spacing is necessary to maintain
certain cable characteristics that if changed, will
decrease the quality of the signal.
Dipole–The element(s) of an antenna that intercepts
the signal and feeds it to the antenna output terminals.
The other elements of the antenna serve as “director”
and “reflector” which direct or reflect the incoming
signal to the dipole element.
Directivity–The ability of an antenna to pick up
signals from one general direction (usually from
the front) and effectively reject those from other
directions (usually from the back and sides). The
front-to-back ratio is one measure of an antenna’s
directivity.
Discharge Unit, Antenna–See Antenna Discharge
Unit.
Distribution Amplifier–An amplifier that is mounted
indoors to boost the strength (level) of the received
signal so that it can be fed to two or more receivers.
Drip Loop–A short, U-shaped loop of a wire (or cable)
immediately adjacent to a house entry point or
electrical connection, so that water will drain off of
the wire and not run into the house or connection.