television antenna
   HOME

TheInfoList



A television antenna (TV aerial) is an
antenna Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio) In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal con ...
specifically designed for use with a
television receiver File:Sony Wega TV set.jpg, A Sony WEGA, Sony Wega CRT television set A television set or television receiver, more commonly called a television, TV, TV set, telly, or tele, is a device that combines a tuner, display, and loudspeakers, for the pu ...
(TV) to receive over-the-air broadcast television signals from a
television station A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television (ATV) operator, that transmits video content and audio content via radio waves directly from a transmitter In elect ...
. Television reception is dependent upon the antenna as well as the
transmitter In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplifi ...
.
Terrestrial television Terrestrial television is a type of television broadcasting in which the television signal is transmitted by radio waves from the terrestrial (Earth-based) transmitter of a television station to a television set, TV receiver having an televisio ...
is broadcast on frequencies from about 47 to 250 
MHz The hertz (symbol: Hz) is the derived unit of frequency Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and an ...
in the
very high frequency Very high frequency (VHF) is the International Telecommunication Union, ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one mete ...
(VHF) band, and 470 to 960 MHz in the
ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300  megahertz (MHz) and 3  gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...

ultra high frequency
(UHF) band
in different countries IN, In or in may refer to: Places * India India (Hindi: ), officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by population, second-most populous country, the List of coun ...
. Television antennas are manufactured in two different types: "indoor" antennas, to be located on top of or next to the
television set A Sony Wega CRT television set A television set or television receiver, more commonly called a television, TV, TV set, telly, or tele, is a device that combines a tuner, display, and loudspeakers, for the purpose of viewing and hearing televis ...
, and "outdoor" antennas, mounted on a
mast Mast, MAST or MASt may refer to: Engineering * Mast (sailing) , a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast , a structure supported by guy-wires * Mooring mast , a structure for docking an airship * Radio m ...
on top of the owner's house. They can also be mounted in a loft or attic, where the dry conditions and increased elevation are advantageous for reception and antenna longevity. Outdoor antennas are more expensive and difficult to install, but are necessary for adequate reception in
fringe ''Fringe'' is an American science fiction on television, science fiction television series created by J. J. Abrams, Alex Kurtzman, and Roberto Orci. It premiered on the Fox Broadcasting Company, Fox network on September 9, 2008, and concluded o ...
areas far from television stations. The most common types of indoor antennas are the
dipole In electromagnetism Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electric charge, electrically charged particles. The electromagnetic force is ca ...
("rabbit ears") and
loop antenna A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing receiving predominantly the magnetic component of the electromagnetic wave, or other electrical conductor usually fed by a balanced source or feeding a balanced load ...

loop antenna
s, and for outdoor antennas the
yagiYagi may refer to: People YAGI Musician, Artist Places *Yagi, Kyoto, in Japan *Yagi (Kashihara), in Nara Prefecture, Japan *Yagi-nishiguchi Station, in Kashihara, Nara, Japan *Kami-Yagi Station, a JR-West Kabe Line station located in 3-chōme, Yagi, ...
, log periodic, and for UHF channels the multi-bay
reflective array antenna Reflective array 'billboard' antenna of the SCR-270 radar, an early US Army radar system. It consists of 32 horizontal half wave dipoles mounted in front of a high screen reflector. With an operating frequency of 106 MHz and a wavelength o ...
.


Description

The purpose of the antenna is to intercept
radio wave Radio waves are a type of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies ma ...
s from the desired
television station A television station is a set of equipment managed by a business, organisation or other entity, such as an amateur television (ATV) operator, that transmits video content and audio content via radio waves directly from a transmitter In elect ...
s and convert them to tiny
radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, alternating electric current or voltage or of a Magnetic_field, magnetic, electric or electromagnetic field or mechanical system in the frequency range from around to around ...
alternating current Alternating current (AC) is an electric current which periodically reverses direction and changes its magnitude continuously with time in contrast to direct current (DC) which flows only in one direction. Alternating current is the form in which ...
s which are applied to the television's tuner, which extracts the television signal. The antenna is connected to the television with a specialized cable designed to carry radio current, called
transmission line . In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmi ...

transmission line
. Earlier antennas used a flat cable called 300
Twin Lead Twins are two offspring In biology, offspring are the young born of living organism, organisms, produced either by a single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny ...
. The standard today is 75 Ω
coaxial cable Coaxial cable, or coax (pronounced ) is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric ( insulating material); many coaxial cables also have a p ...
, which is less susceptible to interference, which plugs into an
F connector The F connector (also F-type connector) is a coaxial RF connector commonly used for "over the air" terrestrial television Terrestrial television is a type of television broadcasting in which the television signal is transmitted by radio wav ...

F connector
or
Belling-Lee connector The Belling-Lee connector (also type 9,52, but largely only in the context of its specification, ''International Electrotechnical Commission, IEC 61169, Part 2: Radio-frequency coaxial connector of type 9,52'') Radio-frequency connectors – Par ...
(depending on region) on the back of the TV. In most countries, television broadcasting is allowed in the
very high frequency Very high frequency (VHF) is the International Telecommunication Union, ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one mete ...
(VHF) band from 47 to 68 MHz, called VHF low band or
band I Band I is a range of radio frequencies within the very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, alternating el ...
in Europe; 174 to 216 MHz, called VHF high band or
band III Band III is the name of the range of radio frequencies within the very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, ...
in Europe, and in the
ultra high frequency Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300  megahertz (MHz) and 3  gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter ...

ultra high frequency
(UHF) band from 470 to 698 MHz, called
band IV Band IV is the name of a radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, alternating electric current or voltage or of a Magnetic_field, magnetic, electric or electromagnetic field or mechanical system in t ...
and V in Europe. The boundaries of each band vary somewhat in different countries. Radio waves in these bands travel by line-of-sight; they are blocked by hills and the visual horizon, limiting a television station's reception area to , depending on terrain.


Analog vs digital

In the previous standard
analog television Analog or analogue may refer to: Computing and electronics * Analog signal An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time-varying quantity, i.e., ''analogous ...
, used before 2006, the VHF and UHF bands required separate tuners in the television receiver, which had separate antenna inputs. The
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...

wavelength
of a
radio wave Radio waves are a type of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies ma ...
equals the speed of light (c) divided by the frequency. The above frequency bands cover a 15:1
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...

wavelength
ratio, or almost 4
octave In music, an octave ( la, octavus: eighth) or perfect octave (sometimes called the Pythagorean interval, diapason) is the interval (music), interval between one musical Pitch (music), pitch and another with double its frequency. The octave relat ...

octave
s. It is difficult to design a single antenna to receive such a wide wavelength range, and there is an octave gap from 216 to 470 MHz between the VHF and UHF frequencies. So traditionally separate antennas (or on outdoor antennas separate sets of elements on a single support boom) have been used to receive the VHF and UHF channels. Starting in 2006, many countries in the world switched from broadcasting using an older
analog television Analog or analogue may refer to: Computing and electronics * Analog signal An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time-varying quantity, i.e., ''analogous ...
standard to newer
digital television Digital television (DTV) is the transmission of television audiovisual Audiovisual (AV) is electronic media possessing both a sound and a visual component, such as slide-tape presentations, films, television programs, corporate conferencing, c ...
(DTV). However generally the same broadcast frequencies are used, so the same antennas used for the older analog television will also receive the new DTV broadcasts. Sellers often claim to supply a special "digital" or "
high-definition television High-definition television (HD or HDTV) describes a television system providing a substantially higher image resolution than the previous generation of technologies. The term has been used since 1936, but in modern times refers to the generation fol ...
" (HDTV) antenna advised as a replacement for an existing
analog television Analog or analogue may refer to: Computing and electronics * Analog signal An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time-varying quantity, i.e., ''analogous ...
antenna; at best this is misinformation to generate sales of unneeded equipment, at worst it may leave the viewer with a UHF-only antenna in a local market (particularly in North America) where some digital stations remain on their original high VHF frequencies.


Reception issues

Places unable to be reached by television broadcast transmitters are known as "black spots" in Australia. In
East Germany East Germany, officially the German Democratic Republic (GDR; german: Deutsche Demokratische Republik, , DDR, ), was a state that existed from 1949 to 1990 in eastern Eastern may refer to: Transportation *China Eastern Airlines, a current C ...
, the areas that could not receive western TV signals were referred to as the '''', or "Valley of the Clueless".


Indoor

Indoor antennas may be mounted on the television itself or stand on a table next to it, connected to the television by a short
feedline In a radio antenna, the feed line (feedline), or feeder, is the cable or other transmission line . In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a con ...
. Due to space constraints, indoor antennas cannot be as large and elaborate as outdoor antennas, and they are not mounted at as high an elevation; for these reasons, indoor antennas generally do not give as good reception as outdoor antennas. They are often perfectly adequate in urban and suburban areas which are usually within the strong radiation "footprint" of local television stations, but in rural fringe reception areas only an outdoor antenna may give adequate reception. A few of the simplest indoor antennas are described below, but a great variety of designs and types exist. Many have a dial on the antenna with a number of different settings to alter the antenna's reception pattern. This should be rotated with the set on while looking at the screen until the best picture is obtained.


Rabbit ears

The oldest and most widely used indoor antenna is the ''rabbit ears'' or ''bunny ears'', which are often provided with new television sets. It is a simple
half-wave dipole In radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an elect ...
antenna used to receive the VHF television bands, consisting in the US of 54 to 88 MHz (
band I Band I is a range of radio frequencies within the very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, alternating el ...
) and 174 to 216 MHz (
band III Band III is the name of the range of radio frequencies within the very high frequency Very high frequency (VHF) is the ITU designation for the range of radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, ...
), with wavelengths of . It is constructed of two telescoping rods attached to a base, which extend out to about length (approximately one quarter wavelength at 54 MHz), and can be collapsed when not in use. For best reception, the rods should be adjusted to be a little less than
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...

wavelength
at the frequency of the television channel being received. However the dipole has a wide
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thro ...
, so often adequate reception is achieved without adjusting the length. The half wave dipole has a low gain of about 2.14 dBi; this means it is not as directional and sensitive to distant stations as a large rooftop antenna, but its wide angle reception pattern may allow it to receive several stations located in different directions without requiring readjustment when the channel is changed. Dipole antennas are bi-directional, that is, they have two
main lobe In a antenna (electronics), radio antenna's radiation pattern, the main lobe, or main beam, is the Side lobe, lobe containing the higher Power (physics), power. This is the lobe that exhibits the greater field strength. The radiation pattern of ...

main lobe
s in opposite directions, 180° apart. Instead of being fixed in position like other antennas, the elements are mounted on ball-and-socket joints and can be adjusted to various angles in a "V" shape, allowing them to be moved out of the way in crowded quarters. Another reason for the V shape is that when receiving channels at the top of the band with the rods fully extended, the antenna elements will typically resonate at their 3rd
harmonic of a vibrating string are harmonics. A harmonic is any member of the harmonic series (music), harmonic series. The term is employed in various disciplines, including music, physics, acoustics, electronic power transmission, radio technology, and ...
. In this mode, the direction of maximum gain (the
main lobe In a antenna (electronics), radio antenna's radiation pattern, the main lobe, or main beam, is the Side lobe, lobe containing the higher Power (physics), power. This is the lobe that exhibits the greater field strength. The radiation pattern of ...

main lobe
) is no longer perpendicular to the rods, but the radiation pattern will have lobes at an angle to the rods, making it advantageous to be able to adjust them to various angles


Whip antenna

Some portable televisions use a
whip antenna A whip antenna is an antenna consisting of a straight flexible wire or rod. The bottom end of the whip is connected to the radio receiver radio in the 1940s. During the golden age of radio, 1925–1955, families gathered to listen to the ho ...
. This consists of a single telescoping rod about long attached to the television, which can be retracted when not in use. It functions as a quarter-wave
monopole antenna monopole antenna of an AM radio station in Chapel Hill, North Carolina. The mast itself is connected to the transmitter and radiates the radio waves. It is mounted on a ceramic insulator to isolate it from the ground. The other terminal of the t ...
. The other side of the feedline is connected to the
ground plane In electrical engineering, a ground plane is an electrically conductive surface, usually connected to electrical ground. The term has two different meanings in separate areas of electrical engineering. In antenna theory, a ground plane is a ...
on the TV's circuit board, which acts as
ground Ground may refer to: * Soil, a mixture of clay, sand and organic matter present on the surface of the Earth * Ground (electricity), the reference point in an electrical circuit from which voltages are measured ** Earthing system, part of an elect ...
. The whip antenna generally has an omnidirectional reception pattern, with maximum sensitivity in directions perpendicular to the antenna axis, and gain similar to the half-wave dipole.


Loop antenna

The UHF channels are often received by a single turn
loop antenna A loop antenna is a radio antenna consisting of a loop or coil of wire, tubing receiving predominantly the magnetic component of the electromagnetic wave, or other electrical conductor usually fed by a balanced source or feeding a balanced load ...

loop antenna
. Since a "rabbit ears" antenna only covers the VHF bands, it is often combined with a UHF loop mounted on the same base to cover all the TV channels.


Flat antenna

Soon after television broadcasting switched from analog to digital broadcasting, indoor antenna marketing evolved beyond the traditional "rabbit ears." Flat antennas are lightweight, thin, and usually square-shaped with the claim of having more omnidirectional reception. They connect to televisions only with a coaxial cable; they may also be sold with a signal amplifier requiring a power source. Internally, the thin, flat square is a loop antenna, with its circular metallic wiring embedded into conductive plastic.


Outdoor

When a higher gain antenna is needed to achieve adequate reception in suburban or fringe reception areas, an outdoor
directional antenna A directional antenna or beam antenna is an antenna which radiates or receives greater power in specific directions allowing increased performance and reduced Interference (communication), interference from unwanted sources. Directional antennas p ...
is usually used. Although most simple antennas have null directions where they have zero response, the directions of useful gain are very broad. In contrast, directional antennas can have an almost unidirectional
radiation pattern pattern of a horn antenna, the bottom shows the omnidirectional pattern of a simple vertical antenna. In the field of Antenna (radio), antenna design the term radiation pattern (or antenna pattern or far-field pattern) refers to the ''direction ...

radiation pattern
so the correct end of the antenna must be pointed at the TV station. As an antenna design provides higher gain (compared to a dipole), the
main lobe In a antenna (electronics), radio antenna's radiation pattern, the main lobe, or main beam, is the Side lobe, lobe containing the higher Power (physics), power. This is the lobe that exhibits the greater field strength. The radiation pattern of ...

main lobe
of the radiation pattern becomes narrower. Outdoor antenna designs are often based on the Yagi-Uda antenna or
log-periodic dipole array A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of Frequency, frequencies. It was invented by John Dunlavy in 1952. The most co ...
(LPDA). These are composed of multiple
half-wave dipole In radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an elect ...
elements, consisting of metal rods approximately half of the
wavelength In physics, the wavelength is the spatial period of a periodic wave—the distance over which the wave's shape repeats. It is the distance between consecutive corresponding points of the same phase (waves), phase on the wave, such as two adjac ...

wavelength
of the television signal, mounted in a line on a support boom. These act as
resonator A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude The amplitude of a Periodic function, periodic Variable (mathematics), variable is a measure of its change ...
s; the electric field of the incoming radio wave pushes the electrons in the rods back and forth, creating
standing wave In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through Sp ...

standing wave
s of oscillating voltage in the rods. The antenna can have a smaller or larger number of rod elements; in general, the more elements the higher the gain and the more directional. Another design, used mainly for UHF reception, is the
reflective array antenna Reflective array 'billboard' antenna of the SCR-270 radar, an early US Army radar system. It consists of 32 horizontal half wave dipoles mounted in front of a high screen reflector. With an operating frequency of 106 MHz and a wavelength o ...
, consisting of a vertical metal screen with multiple dipole elements mounted in front of it. The television broadcast bands are too wide in frequency to be covered by a single antenna, so either separate antennas are used for the VHF and UHF bands, or a combination (combo) VHF/UHF antenna. A VHF/UHF antenna is really two antennas feeding the same feedline mounted on the same support boom. Longer elements which pick up
VHF Very high frequency (VHF) is the ITU designation for the range of radio frequency Radio frequency (RF) is the oscillation rate of an Alternating_current, alternating electric current or voltage or of a Magnetic_field, magnetic, electric or e ...
frequencies are located at the "back" of the boom and often function as a
log-periodic A log-periodic antenna (LP), also known as a log-periodic array or log-periodic aerial, is a multi-element, directional antenna designed to operate over a wide band of Frequency, frequencies. It was invented by John Dunlavy in 1952. The most co ...
antenna. Shorter elements which receive the
UHF Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 megahertz The hertz (symbol: Hz) is the SI derived unit, derived unit of frequency in the International System of Units (SI) and is defin ...

UHF
stations are located at the "front" of the boom and often function as a
Yagi antennaYagi may refer to: People YAGI Musician, Artist Places * Yagi, Kyoto, in Japan * Yagi (Kashihara), in Nara Prefecture, Japan *Yagi-nishiguchi Station, in Kashihara, Nara, Japan *Kami-Yagi Station, a JR-West Kabe Line station located in 3-chōme, Ya ...
. Since directional antennas must be pointed at the transmitting antenna, this is a problem when the television stations to be received are located in different directions. In this case, two or more directional rooftop antennas each pointed at a different transmitter are often mounted on the same mast and connected to one receiver; for best performance filter or matching circuits are used to keep each antenna from degrading the performance of the others connected to the same transmission line. An alternative is to use a single antenna mounted on a ''rotator'', a remote servo system that rotates the antenna to a new direction when a dial next to the television is turned. Sometimes television transmitters are deliberately located such that receivers in a given region need only receive transmissions in a relatively narrow band of the full UHF television spectrum and from the same direction hence allowing the use of a higher gain grouped aerial. File:Mast 1-2.jpg File:UHF TV Antenna 001.JPG, A UHF television antenna File:Rabbit ear dipole antenna rooftop elevated.jpg, A rabbit ear indoor antenna weatherproofed and installed outdoors


Installation

Antennas are commonly placed on , and sometimes in
attic An attic (sometimes referred to as a ''loft'') is a space found directly below the pitched roof of a house or other building; an attic may also be called a ''sky parlor'' or a garret. Because attics fill the space between the ceiling of the to ...
s. Placing an antenna indoors significantly attenuates the level of the available signal. Directional antennas must be pointed at the
transmitter In electronics Electronics comprises the physics, engineering, technology and applications that deal with the emission, flow and control of electrons in vacuum and matter. It uses active devices to control electron flow by amplifier, amplifi ...
they are receiving; in most cases great accuracy is not needed. In a given region it is sometimes arranged that all television transmitters are located in roughly the same direction and use frequencies spaced closely enough that a single antenna suffices for all. A single transmitter location may transmit signals for several channels. CABD (communal antenna broadcast distribution) is a system installed inside a building to receive free-to-air TV/FM signals transmitted via radio frequencies and distribute them to the audience.
Analog television Analog or analogue may refer to: Computing and electronics * Analog signal An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time-varying quantity, i.e., ''analogous ...
signals are susceptible to ghosting in the image, multiple closely spaced images giving the impression of blurred and repeated images of edges in the picture. This is due to the signal being reflected from nearby objects (buildings, tree, mountains); several copies of the signal, of different strengths and subject to different delays, are picked up. This is different for different transmissions. Careful positioning of the antenna can produce a compromise position which minimizes the ghosts on different channels. Ghosting is also possible if multiple antennas connected to the same receiver pick up the same station, especially if the lengths of the cables connecting them to the splitter/merger are different lengths or the antennas are too close together. Analog television is being replaced by digital, which is not subject to ghosting; the same reflected signal that causes ghosting in an analog signal would produce no viewable content at all in digital. However, in this case, interference causes significantly greater image quality degradation.


Rooftop and other outdoor antennas

Aerials are attached to roofs in various ways, usually on a pole to elevate it above the roof. This is generally sufficient in most areas. In some places, however, such as a deep valley or near taller structures, the antenna may need to be placed significantly higher, using a
guyed mast Image:KBRC antenna tower guy wires.JPG, 200 foot (61 m) radio mast of an AM radio station in Mount Vernon, Washington, USA, supported by three sets of 120° guy lines A guyed mast or guyed tower is a tall thin vertical structure that depends on ...
or
mast Mast, MAST or MASt may refer to: Engineering * Mast (sailing) , a vertical spar on a sailing ship * Flagmast, a pole for flying a flag * Guyed mast , a structure supported by guy-wires * Mooring mast , a structure for docking an airship * Radio m ...
. The wire connecting the antenna to indoors is referred to as the ' or ''
drop Drop, DROP, drops or DROPS may refer to: * Drop (liquid) or droplet, a small volume of liquid ** Eye drops, saline (sometimes mydriatic) drops used as medication for the eyes * Drop (unit), a unit of measure of volume * Falling (physics), allowing ...
'', and the longer the downlead is, the greater the signal degradation in the wire. Certain cables may help reduce this tendency. The higher the antenna is placed, the better it will perform. An antenna of higher gain will be able to receive weaker signals from its preferred direction. Intervening buildings, topographical features (mountains), and dense forest will weaken the signal; in many cases, the signal will be reflected such that a usable signal is still available. There are physical dangers inherent to high or complex antennas, such as the structure falling or being destroyed by weather. There are also varying
local ordinance A local ordinance is a law Law is a system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its environment, ...
s which restrict and limit such things as the height of a structure without obtaining permits. For example, in the United States, the
Telecommunications Act of 1996 The Telecommunications Act of 1996 was the first significant overhaul of telecommunications law in more than sixty years, amending the Communications Act of 1934. The Act, signed by President Bill Clinton, represented a major change in American tel ...
allows any homeowner to install "An antenna that is designed to receive local television broadcast signals", but that "masts higher than above the roof-line may be subject to local permitting requirements."


Indoor antennas

As discussed previously, antennas may be placed indoors where signals are strong enough to overcome antenna shortcomings. The antenna is simply plugged into the television receiver and placed conveniently, often on the top of the receiver ("set-top"). Sometimes the position needs to be experimented with to get the best picture. Indoor antennas can also benefit from RF amplification, commonly called a TV booster. Reception form indoor antennas can be problematic in weak signal areas.


Attic installation

Sometimes it is desired not to put an antenna on the roof; in these cases, antennas designed for outdoor use are often mounted in the attic or loft, although antennas designed for attic use are also available. Putting an antenna indoors significantly decreases its performance due to lower elevation above ground level and intervening walls; however, in strong signal areas reception may be satisfactory. One layer of
asphalt Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external ...
shingles Shingles, also known as zoster or herpes zoster, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide stripe either on the left or right side of the body or face. ...
, roof felt, and a
plywood Plywood is a material manufactured from thin layers or "plies" of wood veneer In woodworking, veneer refers to thin slices of wood and sometimes bark, usually thinner than 3 mm (1/8 inch), that typically are glued onto core panels (typica ...

plywood
roof deck 250px, A high level deck in the backyard of a suburban house, in Australia. The decking is a Malaysian timber">Malaysia.html" ;"title="suburban house, in Australia. The decking is a Malaysia">suburban house, in Australia. The decking is a Mala ...
is considered to attenuate the signal to about half.


Multiple antennas, rotators

It is sometimes desired to receive signals from transmitters which are not in the same direction. This can be achieved, for one station at a time, by using a rotator operated by an electric motor to turn the antenna as desired. Alternatively, two or more antennas, each pointing at a desired transmitter and coupled by appropriate circuitry, can be used. To prevent the antennas from interfering with each other, the vertical spacing between the booms must be at least half the wavelength of the lowest frequency to be received (Distance = ). The wavelength of 54 MHz (Channel 2) is (λ × f = c) so the antennas must be a minimum of apart. It is also important that the cables connecting the antennas to the signal splitter/merger be exactly the same length, to prevent
phasing A phaser is an Audio signal processing, electronic sound processor used to audio filter, filter a signal by creating a series of peaks and troughs in the frequency spectrum. The position of the peaks and troughs of the waveform being affected i ...
issues, which cause ghosting with analog reception. That is, the antennas might both pick up the same station; the signal from the one with the shorter cable will reach the receiver slightly sooner, supplying the receiver with two pictures slightly offset. There may be phasing issues even with the same length of down-lead cable.
Bandpass File:Bandpass_Filter.svg, 300px, A medium-complexity example of a band-pass filter. A band-pass filter or bandpass filter (BPF) is a device that passes frequency, frequencies within a certain range and rejects (attenuates) frequencies outside t ...
filters Filter, filtering or filters may refer to: Science and technology Device * Filter (chemistry), a device which separates solids from fluids (liquids or gases) by adding a medium through which only the fluid can pass ** Filter (aquarium), critical ...
or "signal traps" may help to reduce this problem. For side-by-side placement of multiple antennas, as is common in a space of limited height such as an attic, they should be separated by at least one full wavelength of the lowest frequency to be received at their closest point. Often when multiple antennas are used, one is for a range of co-located stations and the other is for a single transmitter in a different direction.


Safety

* TV antennas are good conductors of electricity and attract lightning, acting as a
lightning rod A lightning rod (American English, US, Australian English, AUS) or lightning conductor (British English, UK) is a metal rod mounted on a structure and intended to protect the structure from a lightning strike. If lightning hits the structure, it ...

lightning rod
. The use of a
lightning arrestor A lightning arrester (alternative spelling lightning arrestor) (also called lightning diverter) is a device used on electric power transmission and telecommunication systems to protect the insulator (electrical), insulation and Electrical conducto ...
is usual to protect against this. A large grounding rod connected to both the antenna and the mast or pole is required. * Properly installed masts, especially tall ones, are guyed with
galvanized Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc Zinc is a chemical element with the Symbol (chemistry), symbol Zn and atomic number 30. Zinc is a slightly brittle metal ...
cable; no insulators are needed. They are designed to withstand worst-case weather conditions in the area and positioned so that they do not interfere with power lines if they fall. * There is an inherent danger in being on the rooftop of a house, required for installing or adjusting a television antenna.


See also

*
Radio masts and towers Radio is the technology of signaling and communicating Communication (from Latin ''communicare'', meaning "to share") is the act of developing Semantics, meaning among Subject (philosophy), entities or Organization, groups through the use o ...
, sometimes called Radio and TV antennas *
Satellite dish satellite dish. A satellite dish is a dish-shaped type of parabolic antenna designed to receive or transmit information by radio waves to or from a communication satellite. The term most commonly means a dish which receives direct-broadcast ...
*
Satellite television Satellite television is a service that delivers television programming to viewers by relaying it from a communications satellite orbiting the Earth directly to the viewer's location. The signals are received via an outdoor parabolic antenna common ...
*
Terrestrial television Terrestrial television is a type of television broadcasting in which the television signal is transmitted by radio waves from the terrestrial (Earth-based) transmitter of a television station to a television set, TV receiver having an televisio ...


References


External links


Article on the basic theory of TV aerials and their use

See Which TV Stations You Can Get on a Map


{{DEFAULTSORT:Television Antenna Antennas (radio) Radio electronics Radio frequency antenna types Radio frequency propagation Radio technology
Antenna Antenna (pl. antennas or antennae) may refer to: Science and engineering * Antenna (radio) In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal con ...