Telephone - Invention And Historical Development Of The Telephone, Telephone Set, Telephone Network, Quality Of Telephone Communication
theory million electromagnetic called
The term telephone (from Greek tele, afar, and phone, sound) in a broad sense means a specific type of
Figure 1. Telephone set simplified circuit. Illustration by Hans & Cassidy. Courtesy of Gale Group.
telecommunications which permits people to carry direct conversations over almost any distance. The articulate speech is transmitted in a form of either modulated electric current propagating along conductors or radio waves. The apparatus used for converting the verbal sounds into electromagnetic signals and vice versa is called a telephone set and is also commonly referred to as a telephone. Telephone communication is one of the most widespread and expeditious forms of communication. It has proved to be invaluable for an exchange of information in all areas of human life, whether it is business, government, science, public health, personal services, or social contacts. There were about 200,000 telephones in the world in 1887, approximately 30 million in 1928, 118 million in 1958, and more than 330 million in 1975.
The general concept of the telephone as a system involves a number of elements. First comes a telephone apparatus itself. Next, there is a variety of means for conveying the electromagnetic signals over distances (transmission paths). Third, the transmission paths are arranged in multi-leveled structures (networks) in a way that permits to interconnect (switch) any desired telephone sets upon request. And finally, there are signalling facilities for directing the switching operations, alerting the person called, and clearing the circuits upon the completion of the call.
A scientific and technological discipline which studies and develops all of the telephone-system's constituents is called telephony. Many problems in telephony draw on the principles and techniques of the electromagnetic theory, the theory of linear and nonlinear circuits, the probability theory, and the queuing theory.
Additional Topics
Electrical telecommunication originated in the nineteenth century, with the invention of the tele graph—a method of transferring intelligence between distant places through metallic wires in a form of spaced bursts of electricity. A sender, using a special letter code, produced regulated electrical pulses in a circuit. These signals were converted at the receiving end into a pattern of soun…
A typical telephone instrument (see Figure 1) includes a number of main blocks (a switchhook, a ringer, a dial, a receiver, a transmitter, and a balancing network), which make it capable of numerous operations. 1) It requests the use of the telephone system when the handset is lifted, and signals the system that a call is finished when a caller returns the handset to the cradle. 2) It announces th…
The telephone network's structure may be defined as an entire plant of existing connections between telephone exchanges. It consists of three broad categories: local, exchange area, and long-haul networks. Each telephone is assigned a number indicating its location in the system. The switching network recognizes which telephone initiates the call and which telephone is to receive the call. …
The intelligibility, naturalness, and audibility of transmitted speech are the main requirements for high quality telephone transmission. In technical terms, these requirements mean that: all the harmonic components of the human voice in the frequency range from 300 to 3,400 Hz pass through the communication channel; the loss of a signal during passing the channel does not exceed 30 dB; and the le…
In wireless communication the information is superimposed on a carrier radio signal, which is sent through the air to a receiving location, where the original information is detected and isolated. Cordless, mobile, and cellular telephones perform all functions of the conventional telephone but partially use a radio link instead of wires. The cordless telephone uses low-power radio transmissions on…
Along with the television and the telegraph, the telephone is only a part of a large family of complex telecommunication systems. The past few years have seen the digitalization of the networks. Digital technology uses a simple binary code to represent any signal as a sequence of ones and zeros, somewhat similar to the Morse code, which assigns dot-dash combinations to the letters of the alphabet.…
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