Intelecommunications, arepeater is an electronic device that receives asignal 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 orbaud rate.
There are several different types of repeaters; atelephone repeater is anamplifier in atelephone line, anoptical repeater is anoptoelectronic circuit that amplifies the light beam in anoptical fiber cable; and aradio repeater is aradio receiver andtransmitter that retransmits a radio signal.
Abroadcast relay station is a repeater used inbroadcast radio and television.
When an information-bearing signal passes through acommunication channel, it is progressively degraded due to loss of power. For example, when atelephone call passes through a wiretelephone line, some of the power in theelectric current which represents theaudio signal is dissipated as heat in theresistance of the copper wire. The longer the wire, the more power is lost, and the smaller theamplitude 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 aradio station and areceiver, the weaker theradio signal, and the poorer the reception. A repeater is an electronic device in a communication channel that increases the power of a signal andretransmits it, allowing it to travel further. Since itamplifies the signal, it requires a source ofelectric power.
The term "repeater" originated withtelegraphy in the 19th century, and referred to anelectromechanical device (arelay) used to regenerate telegraph signals.[1][2]
Use of the term has continued intelephony anddata communications.
Incomputer networking, because repeaters work with the actual physical signal, and do not attempt to interpret thedata being transmitted, they operate on thephysical layer, the first layer of theOSI model; a multiportEthernet repeater is usually called ahub.
This is used to increase the range of telephone signals in a telephone line.
They are most frequently used intrunklines that carrylong distance calls. In ananalog telephone line consisting of a pair of wires, it consists of an amplifier circuit made oftransistors which use power from a DC current source to increase the power of thealternating current audio signal on the line. Since the telephone is aduplex (bidirectional) communication system, the wire pair carries twoaudio signals, 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 arefiber-optic cables which use optical repeaters (below).
Before the invention of electronic amplifiers, mechanically coupledcarbon 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.[3] The invention ofaudion tube repeaters around 1916 made transcontinental telephony practical. In the 1930svacuum tube repeaters usinghybrid coils became commonplace, allowing the use of thinner wires. In the 1950snegative impedance gain devices were more popular, and atransistorized version called the E6 repeater was the final major type used in theBell System before the low cost of digital transmission made allvoiceband repeaters obsolete.Frequency frogging repeaters were commonplace in frequency-division multiplexing systems from the middle to late 20th century.
This is a type of telephone repeater used in underwatersubmarine telecommunications cables.
This is used to increase the range of signals in afiber-optic cable. Digital information travels through a fiber-optic cable in the form of short pulses of light. The light is made up of particles calledphotons, which can be absorbed or scattered in the fiber. An optical communications repeater usually consists of aphototransistor which converts the light pulses to an electrical signal, an amplifier to increase the power of the signal, anelectronic filter which reshapes the pulses, and alaser which converts the electrical signal to light again and sends it out the other fiber. However,optical amplifiers are being developed for repeaters to amplify the light itself without the need of converting it to an electric signal first.
This is used to extend the range ofcoverage 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).[2][4] 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.[2]
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 aduplexer can allow the repeater to use oneantenna for both receive and transmit at the same time.
Radio repeaters improve communication coverage in systems using frequencies that typically haveline-of-sight propagation. 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.[5]
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,[6][7] orsatellite network (BGAN,INMARSAT,MSAT) as an alternative path from source to the destination.[8]
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.[9]
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.
Repeaters can be divided into two types depending on the type of data they handle:
This type is used in channels that transmit data in the form of ananalog signal 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 usingfrequency division multiplexing (FDM). Analog repeaters are composed of a linear amplifier, and may includeelectronic filters to compensate for frequency and phase distortion in the line.
Thedigital repeater is used in channels that transmit data bybinarydigital signals, in which the data is in the form of pulses with only two possible values, representing thebinary digits 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 aregenerator.
