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 telephone line consisting of a pair of wires, it consists of an amplifier circuit made of
transistors which use power from a DC current source to increase the power of the
alternating current audio signal on the line. Since the telephone is a
duplex (bidirectional) communication system, the wire pair carries two
audio 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 are
fiber-optic cables 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 repeaters around 1916 made transcontinental telephony practical. In the 1930s
vacuum tube repeaters using
hybrid coils became commonplace, allowing the use of thinner wires. In the 1950s,
negative impedance gain devices were more popular, and a
transistorized version called the E6 repeater was the final major type used in the
Bell System before the low cost of digital transmission made all
voiceband 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 cables.
Optical communications repeater This is used to increase the range of signals in a
fiber-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 called
photons, which can be absorbed or scattered in the fiber. An optical communications repeater usually consists of a
phototransistor which converts the light pulses to an electrical signal, an amplifier to increase the power of the signal, an
electronic filter which reshapes the pulses, and a
laser 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.
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. 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 network (
BGAN,
INMARSAT,
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. 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==