Editing Repeater (section)

===Radio repeater===
[[File:Repeater Talk around channel.png|thumb|A radio communications with a Repeater or a Talkaround channel]]
[[File:Repetitor Guarini.jpg|thumb|Guarini-Foresio's repeater]]
{{main|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).<ref name="slyusar_relay" /><ref>Mattausch J. Telegraphie ohne Draht. Eine Studie. // Zeitschrift für Elektrotechnik. Organ des Elektrotechnischen Vereines in Wien.- Heft 3, 16. Jänner 1898. - XVI. Jahrgang. - S. 35–36.[http://www.slyusar.kiev.ua/all/zeitschriftfrele16.pdf] {{Webarchive|url=https://web.archive.org/web/20170806221424/http://www.slyusar.kiev.ua/all/zeitschriftfrele16.pdf |date=2017-08-06 }}</ref> 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.<ref name="slyusar_relay" />

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]] can allow the repeater to use one [[Antenna (radio)|antenna]] for both receive and transmit at the same time.

:* '''[[Broadcast relay station]], rebroadcastor''' or '''translator''': This is a repeater used to extend the coverage of a radio or television [[Broadcasting|broadcasting station]].  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]]''': This is a specialized [[point-to-point (telecommunications)|point-to-point]] telecommunications link, consisting of a microwave [[radio receiver|receiver]] that receives information over a beam of [[microwave]]s from another relay station in [[Line-of-sight propagation|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]]''': 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]]''': This is a radio repeater for boosting [[cell phone]] reception in a limited area.  The device functions like a small [[cellular base station]], with a directional antenna to receive the signal from the nearest [[cell tower]], 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]] network.  It performs a [[store and forward]] function, passing on packets of information from one node to another.

:* '''[[Amateur radio repeater]]''': 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]]. 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.<ref>{{cite web|url= http://www.taitradioacademy.com/topic/repeater-systems-1/|title= Radio Awareness about Communications Systems - HOW DO REPEATER SYSTEMS WORK?|date= 22 October 2014|publisher= .taitradioacademy.com/|access-date= 2017-08-23|language= en|archive-date= 2017-09-04|archive-url= https://web.archive.org/web/20170904063307/http://www.taitradioacademy.com/topic/repeater-systems-1/|url-status= live}}</ref>

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,<ref>{{cite web  |url=https://basecampconnect.com/radio-interoperability/  |title=Radio Interoperability Communications Systems -  |publisher=basecampconnect.com  |access-date=2017-08-23  |language=en  |archive-date=2017-09-04  |archive-url=https://web.archive.org/web/20170904063824/https://basecampconnect.com/radio-interoperability/  |url-status=live  }}</ref><ref>{{cite web  |url=https://www.codanradio.com/product/3033-telephone-interconnect/  |title=Radio Interoperability - TELEPHONE INTERCONNECT-  |publisher=codanradio.com/  |access-date=2017-08-23  |language=en  |archive-date=2017-09-04  |archive-url=https://web.archive.org/web/20170904064416/https://www.codanradio.com/product/3033-telephone-interconnect/  |url-status=dead  }}</ref> or [[satellite]] network ([[BGAN]], [[INMARSAT]], [[MSAT]]) as an alternative path from source to the destination.<ref>{{cite web|url=http://www.c-at.com/wp-content/uploads/2013/11/Tactical-Voice-Communications-Solutions-for-HLDHLS_rev_B.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.c-at.com/wp-content/uploads/2013/11/Tactical-Voice-Communications-Solutions-for-HLDHLS_rev_B.pdf |archive-date=2022-10-09 |url-status=live |title=   Tactical Voice Communications Solutions for HLD/HLS |publisher=c-at.com|access-date=2017-08-23 |language= en}}</ref>

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 phone|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.<ref>Land mobile radio systems - 2nd ed. Improving and Extending Area Coverage (Englewood Cliffs, NJ : PTR Prentice Hall, 1994) {{ISBN|0131231596}}, p. 67-75.</ref>

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.