The history of Telephone Invention, components of the telephone, Development of the modern instrument and the telephone network.
INTRODUCTION
Telephone, an instrument designed for the simultaneous transmission and reception of the human voice. The telephone is inexpensive, is simple to operate, and offers its users an immediate, personal type of communication that cannot be obtained through any other medium. As a result, it has become the most widely used telecommunications device in the world. Billions of telephones are in use around the world. Alexander Graham Bell, best known for his invention of the telephone, revolutionized communication as we know it.
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His interest in sound technology was deep-rooted and personal, as both his wife and mother were deaf. While there’s some controversy over whether Bell was the true pioneer of the telephone, he secured exclusive rights to the technology and launched the Bell Telephone Company in 1877. Ultimately, the talented scientist held more than 18 patents for his inventions and work in communications. n 1871, Bell started working on the harmonic telegraph — a device that allowed multiple messages to be transmitted over a wire at the same time.
While trying to perfect this technology, which was backed by a group of investors, Bell became preoccupied with finding a way to transmit human voice over wires. By 1875, Bell, with the help of his partner Thomas Watson, had come up with a simple receiver that could turn electricity into sound. Other scientists, including Antonio Meucci and Elisha Gray, were working on similar technologies, and there’s some debate over who should be credited with the invention of the telephone.
It’s said that Bell raced to the patent office to be the first to secure the rights to the discovery. On March 7, 1876, Bell was granted his telephone patent. A few days later, he made the first-ever telephone call to Watson, allegedly uttering the now-famous phrase, “Mr. Watson, come here. I want you.” By 1877, the Bell Telephone Company, which today is known as AT&T, was created. In 1915, Bell made the first transcontinental phone call to Watson from New York City to San Francisco.
HISTORY OF TELEPHONE INVENTION
The concept of the telephone dates back to the string telephone or lover’s telephone that has been known for centuries, comprising two diaphragms connected by a taut string or wire. Sound waves are carried as mechanical vibrations along the string or wire from one diaphragm to the other. The classic example is the tin can telephone, a children’s toy made by connecting the two ends of a string to the bottoms of two metal cans, paper cups or similar items.
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The essential idea of this toy was that a diaphragm can collect voice sounds from the voice sounds for reproduction at a distance. One precursor to the development of the electromagnetic telephone originated in 1833 when Carl Friedrich Gauss and Wilhelm Eduard Weber invented an electromagnetic device for the transmission of telegraphic signals at the University of Göttingen, in Lower Saxony, helping to create the fundamental basis for the technology that was later used in similar telecommunication devices. Gauss’s and Weber’s invention is purported to be the world’s first electromagnetic telegraph.
Credit for the invention of the electric telephone is frequently disputed, and new controversies over the issue have arisen from time to time. Antonio Meucci, Alexander Graham Bell, and Elisha Gray amongst others, have all been credited with the telephone’s invention. The early history of the telephone became and still remains a confusing morass of claims and counterclaims, which were not clarified by the huge number of lawsuits filed in order to resolve the patent claims of the many individuals and commercial competitors.
The Bell and Edison patents, however, were commercially decisive, because they dominated telephone technology and were upheld by court decisions in the United States. The modern telephone is the result of the work of many people. Alexander Graham Bell was, however, the first to patent the telephone, as an “apparatus for transmitting vocal or other sounds telegraphically”. Bell has most often been credited as the inventor of the first practical telephone.
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Johann Philipp Reis coined the term “telephon”. Models of it were sent abroad, to London, Dublin, Tiflis, and other places. It became a subject for popular lectures, and an article for scientific cabinets. Edison credited him as the “first inventor of the telephone.” The Italian-American inventor and businessman Antonio Meucci has been recognized by the U.S. House of Representatives for his contributory work on the telephone.
Components Of the Telephone
As it has since its early years, the telephone instrument is made up of the following functional components: a power source, a switch hook, a dialer, a ringer, a transmitter, a receiver, and an anti-sidetone circuit. These components are described in turn below:
- Power source: The first sources were batteries located in the telephone instruments themselves, but since the 1890s current has been generated at the local switching office. The current is supplied through a two-wire circuit called the local loop. The standard voltage is 48 volts. Cordless telephones represent a return to individual power sources in that their low-wattage radio transmitters are powered by a small (e.g., 3.6-volt) battery located in the portable handset. When the telephone is not in use, the battery is recharged through contacts with the base unit. The base unit is powered by a transformer connection to a standard electric outlet.
- Switch hook: When the telephone is “on hook,” contact with the local loop is broken. When it is “off hook” (i.e., when the handset is lifted from the cradle), contact is restored, and current flows through the loop. The switching office signals restoration of contact by transmitting a low-frequency “dial tone”—actually two simultaneous tones of 350 and 440 hertz.
- Dialer: The dialer is used to enter the number of the party that the user wishes to call. Signals generated by the dialer activate switches in the local office, which establish a transmission path to the called party. Dialers are of the rotary and push-button types.
- Ringer: In modern electronic ringers, introduced in the 1980s, the ringer current is passed through an oscillator, which adjusts the current to the precise frequency required to activate a piezoelectric transducer—a device made of a crystalline material that vibrates in response to an electric current. The transducer may be coupled to a small loudspeaker, which can be adjusted for volume. The ringer circuit remains connected to the local loop even when the telephone is on hook.
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A larger voltage is necessary to activate the ringer because the ringer circuit is made with a high electrical impedance in order to avoid draining power from the transmitter-receiver circuit when the telephone is in use. A capacitor prevents direct current from passing through the ringer once the handset has been lifted off the switch hook.
- Transmitter: In modern electret transmitters, developed in the 1970s, the carbon layer is replaced by a thin plastic sheet that has been given a conductive metallic coating on one side. The plastic separates that coating from another metal electrode and maintains an electric field between them. Vibrations caused by speech produce fluctuations in the electric field, which in turn produce small variations in voltage. The voltages are amplified for transmission over the telephone line.
- Receiver: The receiver is located in the earpiece of the telephone’s handset. Operating on electromagnetic principles that were known in Bell’s Day, it converts fluctuating electric current into sound waves that reproduce human speech. Fundamentally, it consists of two parts: a permanent magnet, having pole pieces wound with coils of insulated fine wire, and a diaphragm driven by magnetic material that is supported near the pole pieces. Speech currents passing through the coils vary the attraction of the permanent magnet for the diaphragm, causing it to vibrate and produce sound waves.
- Anti-sidetone circuit: The anti-sidetone circuit also matches the low electrical impedance of the telephone instrument’s circuits to the higher electrical impedance of the telephone line. Impedance matching allows a more efficient flow of current through the system.
Development of the modern instrument
Modern telephone instruments are largely electronic. Wire coils that performed multiple functions in older sets have been replaced by integrated circuits that are powered by the line voltage. Mechanical bell ringers have given way to electronic ringers. The carbon transmitter dating from Edison’s time has been replaced by electret microphones, in which sound waves cause a thin, metal-coated plastic diaphragm to vibrate, producing variations in an electric field across a tiny air gap between the diaphragm and an electrode.
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The telephone dial has given way to the keypad, which can usually be switched to generate either pulses similar to those of the dial mechanism or dual-tone signals as in AT&T’s Touch-Tone system. Finally, a number of other features have become available on the telephone instrument, including last-number recall and speed-dialing of multiple telephone numbers.
The Telephone Network
In order to understand the many concepts represented in the public switched telephone network (PSTN), it is helpful to review the processes that take place in the making of a single call on a traditional wired telephone. To make a call, a telephone subscriber begins by taking the telephone “off-hook”—in the process, signaling the local central office that service is requested. The central office, which has been monitoring the telephone line continuously (a process known as attending), responds with a dial tone.
Upon receiving the dial tone, the customer enters the called party’s telephone number. The central office stores the entered number, translates the number into an equipment location and a path to that location, and tests whether the called party’s line is already in use (or “busy”). The called party’s number may lie in the same central office (in which case the call is designated intraoffice), or it may lie in another central office (requiring an interoffice call).
If the call is intraoffice, the central office switch will handle the entire call process. If the call is interoffice, it will be directed either to a nearby central office or to a distant central office via a long-distance network. In the case of interoffice calls, a separate signaling network is employed to coordinate the call progression through a multitude of switches and telephone trunks.
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From the example described above, it is evident that telephone systems consist of four major components:
- Switching, between telephone sets and between trunks, as required.
- Signaling, between the telephone sets and the central offices as well as between central offices when needed.
- Transmission, between the central switching office and subscribers’ telephone sets and also between central offices.
CONCLUTION
The first mobile and portable subscriber units for cellular systems were large and heavy. With significant advances in component technology, though, the weight and size of portable transceivers have been significantly reduced.