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In
telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...
, a repeater is an electronic device that receives a
signal A signal is both the process and the result of transmission of data over some media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processing, information theory and biology. In ...
and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some types of repeaters broadcast an identical signal, but alter its method of transmission, for example, on another frequency or
baud rate In a digitally modulated signal or a line code, symbol rate, modulation rate or baud is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in ''baud'' ...
. There are several different types of repeaters; a telephone repeater is an
amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power su ...
in a
telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or oth ...
, an
optical repeater An optical communications repeater is used in a fiber-optic communications system to regenerate an optical signal. Such repeaters are used to extend the reach of optical communications links by overcoming loss due to attenuation of the optical f ...
is an
optoelectronic Optoelectronics (or optronics) is the study and application of electronic devices and systems that find, detect and control light, usually considered a sub-field of photonics. In this context, ''light'' often includes invisible forms of radia ...
circuit that amplifies the light beam in an
optical fiber cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with p ...
; and a
radio repeater A radio repeater is a combination of a radio receiver and a radio transmitter that receives a signal and retransmits it, so that two-way radio signals can cover longer distances. A repeater sited at a high elevation can allow two mobile stations ...
is a
radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. ...
and
transmitter In electronics and telecommunications, a radio transmitter or just transmitter (often abbreviated as XMTR or TX in technical documents) is an electronic device which produces radio waves with an antenna (radio), antenna with the purpose of sig ...
that retransmits a radio signal. A
broadcast relay station A broadcast relay station, also known as a satellite station, relay transmitter, broadcast translator (U.S.), re-broadcaster (Canada), repeater ( two-way radio) or complementary station (Mexico), is a broadcast transmitter which repeats (or tr ...
is a repeater used in broadcast radio and television.


Overview

When an information-bearing signal passes through a
communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for infor ...
, it is progressively degraded due to loss of power. For example, when a
telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...
passes through a wire
telephone line A telephone line or telephone circuit (or just line or circuit industrywide) is a single-user circuit on a telephone communication system. It is designed to reproduce speech of a quality that is understandable. It is the physical wire or oth ...
, some of the power in the
electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
which represents the
audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals or a series of binary numbers for Digital signal (signal processing), digital signals. Audio signals have frequencies i ...
is dissipated as heat in the resistance of the copper wire. The longer the wire, the more power is lost, and the smaller the
amplitude The amplitude of a periodic variable is a measure of its change in a single period (such as time or spatial period). The amplitude of a non-periodic signal is its magnitude compared with a reference value. There are various definitions of am ...
of the signal at the far end. So with a long enough wire the call will not be audible at the other end. Similarly, the greater the distance between a
radio station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based rad ...
and a receiver, the weaker the
radio signal Radio waves (formerly called Hertzian waves) are a type of electromagnetic radiation with the lowest frequencies and the longest wavelengths in the electromagnetic spectrum, typically with frequencies below 300 gigahertz (GHz) and wavelengths g ...
, and the poorer the reception. A repeater is an electronic device in a communication channel that increases the power of a signal and retransmits it, allowing it to travel further. Since it amplifies the signal, it requires a source of
electric power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...
. The term "repeater" originated with
telegraphy Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas pi ...
in the 19th century, and referred to an
electromechanical Electromechanics combine processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focus on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each ...
device (a
relay A relay Electromechanical relay schematic showing a control coil, four pairs of normally open and one pair of normally closed contacts An automotive-style miniature relay with the dust cover taken off A relay is an electrically operated switc ...
) used to regenerate telegraph signals. Use of the term has continued in
telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunications services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is ...
and
data communication Data communication, including data transmission and data reception, is the transfer of data, transmitted and received over a point-to-point or point-to-multipoint communication channel. Examples of such channels are copper wires, optic ...
s. In
computer networking A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or b ...
, because repeaters work with the actual physical signal, and do not attempt to interpret the
data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...
being transmitted, they operate on the
physical layer In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first and lowest layer: the layer most closely associated with the physical connection between devices. The physical layer provides an electrical, mechani ...
, the first layer of the
OSI model The Open Systems Interconnection (OSI) model is a reference model developed by the International Organization for Standardization (ISO) that "provides a common basis for the coordination of standards development for the purpose of systems inter ...
; a multiport
Ethernet Ethernet ( ) is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 198 ...
repeater is usually called a hub.


Types


Telephone repeater

This is used to increase the range of telephone signals in a telephone line. :* Land line repeater They are most frequently used in trunklines that carry long distance calls. In an
analog Analog or analogue may refer to: Computing and electronics * Analog signal, in which information is encoded in a continuous variable ** Analog device, an apparatus that operates on analog signals *** Analog electronics, circuits which use analog ...
telephone line consisting of a pair of wires, it consists of an amplifier circuit made of
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
s which use power from a DC current source to increase the power of the
alternating current Alternating current (AC) is an electric current that 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 w ...
audio signal on the line. Since the telephone is a duplex (bidirectional) communication system, the wire pair carries two
audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals or a series of binary numbers for Digital signal (signal processing), digital signals. Audio signals have frequencies i ...
s, one going in each direction. So telephone repeaters have to be bilateral, amplifying the signal in both directions without causing feedback, which complicates their design considerably. Telephone repeaters were the first type of repeater and were some of the first applications of amplification. The development of telephone repeaters between 1900 and 1915 made long-distance phone service possible. Now, most telecommunications cables are
fiber-optic cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with p ...
s which use optical repeaters (below). Before the invention of electronic amplifiers, mechanically coupled carbon microphones were used as amplifiers in telephone repeaters. After the turn of the 20th century it was found that negative resistance mercury lamps could amplify, and they were used. The invention of
audion tube The Audion was an electronic detecting or amplifying vacuum tube invented by American electrical engineer Lee de Forest as a diode in 1906.De Forest patented a number of variations of his detector tubes starting in 1906. The patent that most cle ...
repeaters around 1916 made transcontinental telephony practical. In the 1930s
vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...
repeaters using
hybrid coil A hybrid transformer (also known as a bridge transformer, hybrid coil, or just hybrid) is a type of directional coupler which is designed to be configured as a circuit having four ports that are conjugate in pairs, implemented using one or mo ...
s became commonplace, allowing the use of thinner wires. In the 1950s negative impedance gain devices were more popular, and a
transistor A transistor is a semiconductor device used to Electronic amplifier, amplify or electronic switch, switch electrical signals and electric power, power. It is one of the basic building blocks of modern electronics. It is composed of semicondu ...
ized version called the E6 repeater was the final major type used in the
Bell System The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the AT&T Corporation, American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America fo ...
before the low cost of digital transmission made all
voiceband A voice frequency (VF) or voice band is the range of audio frequencies used for the transmission of speech. Frequency band In telephony, the usable voice frequency band ranges from approximately 300 to 3400  Hz. It is for this reason th ...
repeaters obsolete. Frequency frogging repeaters were commonplace in frequency-division multiplexing systems from the middle to late 20th century. :* Submarine cable repeater This is a type of telephone repeater used in underwater
submarine telecommunications cable A submarine communications cable is a cable laid on the seabed between land-based stations to carry telecommunication signals across stretches of ocean and sea. The first submarine communications cables were laid beginning in the 1850s and car ...
s.


Optical communications repeater

This is used to increase the range of signals in a
fiber-optic cable A fiber-optic cable, also known as an optical-fiber cable, is an assembly similar to an electrical cable but containing one or more optical fibers that are used to carry light. The optical fiber elements are typically individually coated with p ...
. Digital information travels through a fiber-optic cable in the form of short pulses of light. The light is made up of particles called
photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless particles that can ...
s, which can be absorbed or scattered in the fiber. An optical communications repeater usually consists of a
phototransistor A photodiode is a semiconductor diode sensitive to photon radiation, such as visible light, infrared or ultraviolet radiation, X-rays and gamma rays. It produces an electrical current when it absorbs photons. This can be used for detection and me ...
which converts the light pulses to an electrical signal, an amplifier to increase the power of the signal, an
electronic filter Electronic filters are a type of signal processing filter in the form of electrical circuits. This article covers those filters consisting of lumped-element model, lumped electronic components, as opposed to distributed-element filters. That ...
which reshapes the pulses, and a
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word ''laser'' originated as an acronym for light amplification by stimulated emission of radi ...
which converts the electrical signal to light again and sends it out the other fiber. However,
optical amplifier An optical amplifier is a device that amplifies an optical signal directly, without the need to first convert it to an electrical signal. An optical amplifier may be thought of as a laser without an optical cavity, or one in which feedback fro ...
s are being developed for repeaters to amplify the light itself without the need of converting it to an electric signal first.


Radio repeater

This is used to extend the range of coverage of a radio signal. The history of radio relay repeaters began in 1898 from the publication by Johann Mattausch in Austrian Journal Zeitschrift für Electrotechnik (v. 16, 35 - 36). But his proposal "Translator" was primitive and not suitable for use. The first relay system with radio repeaters, which really functioned, was that invented in 1899 by Emile Guarini-Foresio. A radio repeater usually consists of a radio receiver connected to a radio transmitter. The received signal is amplified and retransmitted, often on another frequency, to provide coverage beyond the obstruction. Usage of a
duplexer A duplexer is an electronic device that allows bi-directional ( duplex) communication over a single path. In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. ...
can allow the repeater to use one antenna for both receive and transmit at the same time. :*
Broadcast relay station A broadcast relay station, also known as a satellite station, relay transmitter, broadcast translator (U.S.), re-broadcaster (Canada), repeater ( two-way radio) or complementary station (Mexico), is a broadcast transmitter which repeats (or tr ...
, rebroadcastor or translator: This is a repeater used to extend the coverage of a radio or television
broadcasting station Radio broadcasting is the broadcasting of audio (sound), sometimes with related metadata, by radio waves to radio receivers belonging to a public audience. In terrestrial radio broadcasting the radio waves are broadcast by a land-based radio ...
. It consists of a secondary radio or television transmitter. The signal from the main transmitter often comes over leased telephone lines or by microwave relay. :*
Microwave relay Microwave transmission is the transmission of information by electromagnetic waves with wavelengths in the microwave frequency range of 300 MHz to 300 GHz (1 m - 1 mm wavelength) of the electromagnetic spectrum. Microwave signal ...
: This is a specialized point-to-point telecommunications link, consisting of a microwave receiver that receives information over a beam of
microwave Microwave is a form of electromagnetic radiation with wavelengths shorter than other radio waves but longer than infrared waves. Its wavelength ranges from about one meter to one millimeter, corresponding to frequency, frequencies between 300&n ...
s from another relay station in line-of-sight distance, and a microwave transmitter which passes the information on to the next station over another beam of microwaves. Networks of microwave relay stations transmit telephone calls, television programs, and computer data from one city to another over continent-wide areas. ::*
Passive repeater A passive repeater or passive radio link deflection, is a reflective or sometimes refractive panel or other object that assists in closing a radio or microwave link, in places where an obstacle in the signal path blocks any direct, line of si ...
: This is a microwave relay that simply consists of a flat metal surface to reflect the microwave beam in another direction. It is used to get microwave relay signals over hills and mountains when it is not necessary to amplify the signal. :*
Cellular repeater A cellular repeater (also known as cell phone signal booster or cell phone signal amplifier) is a type of bi-directional amplifier used to improve cell phone reception. A cellular repeater system commonly consists of a donor Antenna (radio), anten ...
: This is a radio repeater for boosting
cell phone A mobile phone or cell phone is a portable telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones ( landline phones). This radio ...
reception in a limited area. The device functions like a small
cellular base station A cell site, cell phone tower, cell base tower, or cellular base station is a cellular frequencies, cellular-enabled mobile device site where antenna (electronics), antennas and electronic communications equipment are placed (typically on a Rad ...
, with a directional antenna to receive the signal from the nearest
cell tower A cell site, cell phone tower, cell base tower, or cellular base station is a cellular-enabled mobile device site where antennas and electronic communications equipment are placed (typically on a radio mast, tower, or other raised structure) ...
, an amplifier, and a local antenna to rebroadcast the signal to nearby cell phones. It is often used in downtown office buildings. :* Digipeater: A repeater node in a
packet radio In digital radio, packet radio is the application of packet switching techniques to digital radio communications. Packet radio uses a packet switching Communication protocol, protocol as opposed to circuit switching or message switching protocols ...
network. It performs a
store and forward Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node in ...
function, passing on packets of information from one node to another. :*
Amateur radio repeater An amateur radio repeater is an electronic device that receives a weak or low-level amateur radio signal and retransmits it at a higher level or higher power, so that the signal can cover longer distances without degradation. Many repeaters a ...
: Used by amateur radio operators to enable two-way communication across an area which would otherwise be difficult by point-to-point on VHF and UHF. These repeaters are set up and maintained by individual operators or clubs, and are generally available for any licensed amateur to use. A hill or mountaintop location is a preferable location to construct a repeater, as it will maximize the usability across a large area. Radio repeaters improve communication coverage in systems using frequencies that typically have
line-of-sight propagation Line-of-sight propagation is a characteristic of electromagnetic radiation or acoustic wave propagation which means waves can only travel in a direct visual path from the source to the receiver without obstacles. Electromagnetic transmission in ...
. Without a repeater, these systems are limited in range by the curvature of the Earth and the blocking effect of terrain or high buildings. A repeater on a hilltop or tall building can allow stations that are out of each other's line-of-sight range to communicate reliably. Radio repeaters may also allow translation from one set of radio frequencies to another, for example to allow two different public service agencies to interoperate (say, police and fire services of a city, or neighboring police departments). They may provide links to the public switched telephone network as well, or
satellite A satellite or an artificial satellite is an object, typically a spacecraft, placed into orbit around a celestial body. They have a variety of uses, including communication relay, weather forecasting, navigation ( GPS), broadcasting, scient ...
network (
BGAN The Broadband Global Area Network (BGAN) is a global satellite network with telephony owned by Inmarsat using portable terminals. The terminals are normally used to connect a laptop computer to broadband Internet in remote locations, although as ...
,
INMARSAT Inmarsat is a British communications satellite, satellite telecommunications company, offering global mobile services. It provides telephone and data services to users worldwide, via portable or mobile terminals which communicate with groun ...
, MSAT) as an alternative path from source to the destination. Typically a repeater station listens on one frequency, A, and transmits on a second, B. All mobile stations listen for signals on channel B and transmit on channel A. The difference between the two frequencies may be relatively small compared to the frequency of operation, say 1%. Often the repeater station will use the same antenna for transmission and reception; highly selective filters called "duplexers" separate the faint incoming received signal from the billions of times more powerful outbound transmitted signal. Sometimes separate transmitting and receiving locations are used, connected by a wire line or a radio link. While the repeater station is designed for simultaneous reception and transmission, mobile units need not be equipped with the bulky and costly duplexers, as they only transmit or receive at any time. Mobile units in a repeater system may be provided with a "talkaround" channel that allows direct mobile-to-mobile operation on a single channel. This may be used if out of reach of the repeater system, or for communications not requiring the attention of all mobiles. The "talkaround" channel may be the repeater output frequency; the repeater will not retransmit any signals on its output frequency.Land mobile radio systems - 2nd ed. Improving and Extending Area Coverage (Englewood Cliffs, NJ : PTR Prentice Hall, 1994) , p. 67-75. An engineered radio communication system designer will analyze the coverage area desired and select repeater locations, elevations, antennas, operating frequencies and power levels to permit a predictable level of reliable communication over the designed coverage area.


Data handling

Repeaters can be divided into two types depending on the type of data they handle:


Analog repeater

This type is used in channels that transmit data in the form of an
analog signal An analog signal (American English) or analogue signal (British and Commonwealth English) is any continuous-time signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the ins ...
in which the voltage or current is proportional to the amplitude of the signal, as in an audio signal. They are also used in trunklines that transmit multiple signals using
frequency division multiplexing In telecommunications, frequency-division multiplexing (FDM) is a technique by which the total bandwidth available in a communication medium is divided into a series of non-overlapping frequency bands, each of which is used to carry a separate ...
(FDM). Analog repeaters are composed of a linear amplifier, and may include
electronic filter Electronic filters are a type of signal processing filter in the form of electrical circuits. This article covers those filters consisting of lumped-element model, lumped electronic components, as opposed to distributed-element filters. That ...
s to compensate for frequency and phase distortion in the line.


Digital repeater

The digital repeater is used in channels that transmit data by
binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical op ...
digital signal A digital signal is a signal that represents data as a sequence of discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog signal, which represents continuous values; ...
s, in which the data is in the form of pulses with only two possible values, representing the
binary digit Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two values (0 and 1) for each digit * Binary function, a function that takes two arguments * Binary operation, a mathematical o ...
s 1 and 0. A digital repeater amplifies the signal, and it also may retime, resynchronize, and reshape the pulses. A repeater that performs the retiming or resynchronizing functions may be called a
regenerator Regenerator may refer to: * Regenerative heat exchanger, a type of heat exchanger * Regenerator (band), an independent record label set up in 2001 * Regenerator (''Resident Evil''), an enemy creature in the 2005 video game ''Resident Evil 4'' * ' ...
.


See also

*
12-channel carrier system In the U.S. telephone network, the 12-channel carrier system was an early frequency-division multiplexing system standard, used to carry multiple telephone calls on a single twisted pair of wires, mostly for short to medium distances. In this syst ...
*
ADSL loop extender A DSL loop extender is a device that a telephone company can place between subscriber premises equipment and central office interfaces to extend the distance and increase the channel capacity of digital subscriber line (DSL) connections. ADSL repeat ...
* Complementary ground component *
Fiber media converter A fiber media converter is a simple Computer Network, networking device that makes it possible to connect two dissimilar media types such as twisted pair with Optical fiber, fiber optic cabling. They were introduced to the industry in the 1990 ...
* PLC carrier repeating station *
Relay (disambiguation) A relay is an electric switch operated by a signal in one circuit to control another circuit. Relay may also refer to: Electrical engineering * Protective relay, a device designed to trip a circuit breaker when a fault is detected. Historical * ...
*
Repeater insertion Repeater insertion is a technique used to reduce time delays associated with long wire lines in integrated circuits. This technique involves cutting the long wire into one or more shorter wires, and then inserting a repeater between each pair of ne ...
in integrated circuits *
Signal strength In telecommunications, particularly in radio frequency engineering, signal strength is the transmitter power output as received by a reference antenna at a distance from the transmitting antenna. High-powered transmissions, such as those used i ...
*
Transponder In telecommunications, a transponder is a device that, upon receiving a signal, emits a different signal in response. The term is a blend of ''transmitter'' and ''responder''. In air navigation or radio frequency identification, a flight trans ...
*
Wireless distribution system A wireless distribution system (WDS) is a system enabling the wireless interconnection of access points in an IEEE 802.11 network. It allows a wireless network to be expanded using multiple access points without the traditional requirement for a ...
*
Wireless repeater A wireless repeater (also called wireless range extender or wifi extender) is a device that takes an existing signal from a wireless router or wireless access point and rebroadcasts it to create a second network. When two or more hosts have to ...


References


External links

* The
Bell system The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the AT&T Corporation, American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America fo ...
technical journal
Repeaters and Equalizers for the SD Submarine Cable System

Amateur Radio Repeaters in India

Amateur Radio Repeaters in Europe
{{Two-way radio Telecommunications equipment Mobile technology Radio electronics Physical layer protocols