L-carrier
The L-carrier system was one of a series of carrier systems developed by AT&T for high-capacity transmission for long-distance communications. Over a period from the late 1930s to the 1970s, the system evolved in six significant phases of development, designated by Bell System engineers as L-1 through L-5, and L-5E. Coaxial cable was the principal transmission medium in all stages, initially lending the system another description i.e. the ''coaxial system''.E.L. Green, ''The Coaxial Cable System'', Bell Laboratories Record 15(9) p274 (May 1937) It was the successor to a series of previous carrier systems, typically identified by capital letters. In the 1960s the system was hardened against the dangers of the Cold War using complete placement of all terminal and repeater equipment in hardened underground vaults. Initial development and testing of the coaxial system took place between 1935 and 1937 on a test bed of a 95-mile two-way coaxial cable between locations in New York Cit ...
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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 signal. This allows a single transmission medium such as a microwave radio link, cable or optical fiber to be shared by multiple independent signals. Another use is to carry separate serial bits or segments of a higher rate signal in parallel. The most common example of frequency-division multiplexing is radio and television broadcasting, in which multiple radio signals at different frequencies pass through the air at the same time. Another example is cable television, in which many television channels are carried simultaneously on a single cable. FDM is also used by telephone systems to transmit multiple telephone calls through high capacity trunklines, communications satellites to transmit multiple channels of data on uplink and downl ...
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Carrier System
A carrier system is a telecommunications system that transmits information, such as the voice signals of a telephone call and the video signals of television, by modulation of one or multiple carrier signals above the principal voice frequency or data rate.Western Electric (1969) ''Fundamentals of Telephone Communication Systems'', p.16.2 Carrier systems typically transmit multiple channels of communication simultaneously over the shared medium using various forms of multiplexing. Prominent multiplexing methods of the carrier signal are time-division multiplexing (TDM) and frequency-division multiplexing (FDM). A cable television system is an example of frequency-division multiplexing. Many television programs are carried simultaneously on the same coaxial cable by sending each at a different frequency. Multiple layers of multiplexing may ultimately be performed upon a given input signal. For example, in the public switched telephone network, many telephone calls are sent over sha ...
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T-carrier
The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell System, and could transmit up to 24 telephone calls simultaneously over a single transmission line of copper wire. Subsequent specifications carried multiples of the basic T1 (1.544 Mbit/s) data rates, such as T2 (6.312 Mbit/s) with 96 channels, T3 (44.736 Mbit/s) with 672 channels, and others. Although a ''T2'' was defined as part of AT&T's T-carrier system, which defined five levels, T1 through T5, only the T1 and T3 were commonly in use.1999 ad: On the left, in an aisle seat, a man who very much "filled" his airline seat while on the right side of the aisle is a height-challenged man whose shoe toes barely reach the floor Transmission System 1 The T-carrier is a hardware specification for carrying multiple time-division mul ...
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Television Network
A television network or television broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or multichannel video programming distributor, pay television providers. Until the mid-1980s, television broadcast programming, programming in most countries of the world was dominated by a small number of terrestrial networks. Many early television networks (such as NBC, the Australian Broadcasting Corporation, ABC, or the BBC) evolved from earlier radio networks. Overview In countries where most networks broadcast identical, centrally originated content to all of their stations and where most individual television transmitters therefore operate only as large "broadcast relay station, repeater stations", the terms "television network", "television channel" (a numeric identifier or radio frequency) and "television station" have become mostly interchangeable in everyday language, wit ...
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Single-sideband Modulation
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver. Basic concept Radio transmitters work by mixing a radio frequency (RF) signal of a specific frequency, the carrier wave, with the audio signal to be broadcast. In AM transmitters this mixing usually takes place in the final RF amplifier (high level modulation). It is less common and much less efficient to do the mixing at low power and then amplify it in a linear ampl ...
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Single Sideband
In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver. Basic concept Radio transmitters work by mixing a radio frequency (RF) signal of a specific frequency, the carrier wave, with the audio signal to be broadcast. In AM transmitters this mixing usually takes place in the final RF amplifier (high level modulation). It is less common and much less efficient to do the mixing at low power and then amplify it in a linear ampl ...
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AT&T Long Lines
AT&T Communications, Inc., was a division of the AT&T Corporation that, through 23 subsidiaries, provided interexchange carrier and long-distance calling, long-distance telephone services. History AT&T Long Lines The American Telephone & Telegraph Long Lines wire, cable, and microwave radio relay network provided long-distance services to AT&T and its customers. The connection to other countries from the United States began here. By the 1970s, 95% of distance and 70% of intercity telephone calls in the United States were carried by AT&T. Before utilizing microwave relay and coaxial cables, AT&T used lines for long-distance calling, long-distance service. In 1911, the system connected New York to Denver. The introduction of repeater towers allowed such connections to reach across North America. In the 1930s the company experimented with long-distance coaxial cable. The first long-distance L-carrier coaxial link in 1936 connected Philadelphia and New York City. With impr ...
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12-channel Carrier System
{{Unreferenced, date= October 2009 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 system twelve voice channels are multiplexed in a high frequency carrier and passed through a balanced pair trunk line similar to those used for individual voice frequency connections. The original system is obsolete today, but the multiplexing of voice channels in units of 12 or 24 channels in modern digital trunk lines such as T-1 is a legacy of the system. History The twelve channel scheme was first devised in the early 1930s to provide a line spectrum covering 60 to 108 kHz for the Type J Carrier Telephone System, an equivalent four wire (on two wire facilities) open wire carrier that was used almost exclusively for interstate long haul toll telephony. This became the basic building block, the "cha ...
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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 protective outer sheath or jacket. The term ''coaxial'' refers to the inner conductor and the outer shield sharing a geometric axis. Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses. It is used in such applications as telephone trunk lines, broadband internet networking cables, high-speed computer data busses, cable television signals, and connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line. Coaxial cable was used in the first (1858) and followin ...
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FDM Drawings 2
FDM may refer to: Science and technology * Fat in dry matter, a food content measurement * Finite difference method, a numerical method for solving differential equations * Free Download Manager, a download manager for Windows and macOS * Frequency-division multiplexing, a signal multiplexing method * Functional Database Model, a technique in business and financial planning * Fused deposition modeling, a 3-D printing technique, see: FFF * Fascial distortion model, an anatomical and physiological model of medicine Other * fdm (software), a program to fetch, filter and deliver email * FDM Group, a British IT service company * Federation of Danish Motorists * Funeral doom metal * First degree murder Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human with malice aforethought. ("The killing of another person without justification or excuse, especially the c ...

FDM Drawings 3
FDM may refer to: Science and technology * Fat in dry matter, a food content measurement * Finite difference method, a numerical method for solving differential equations * Free Download Manager, a download manager for Windows and macOS * Frequency-division multiplexing, a signal multiplexing method * Functional Database Model, a technique in business and financial planning * Fused deposition modeling, a 3-D printing technique, see: FFF * Fascial distortion model, an anatomical and physiological model of medicine Other * fdm (software), a program to fetch, filter and deliver email * FDM Group, a British IT service company * Federation of Danish Motorists * Funeral doom metal * First degree murder Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human with malice aforethought. ("The killing of another person without justification or excuse, especially the c ...

FDM Drawings 1
FDM may refer to: Science and technology * Fat in dry matter, a food content measurement * Finite difference method, a numerical method for solving differential equations * Free Download Manager, a download manager for Windows and macOS * Frequency-division multiplexing, a signal multiplexing method * Functional Database Model, a technique in business and financial planning * Fused deposition modeling, a 3-D printing technique, see: FFF * Fascial distortion model, an anatomical and physiological model of medicine Other * fdm (software), a program to fetch, filter and deliver email * FDM Group, a British IT service company * Federation of Danish Motorists * Funeral doom metal * First degree murder Murder is the unlawful killing of another human without justification or valid excuse, especially the unlawful killing of another human with malice aforethought. ("The killing of another person without justification or excuse, especially the c ...