Telephone

A telephone is a telecommunications device that allowed two or more users to conduct a conversation when they are too far apart to be heard directly. a telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables together with other communication channels to another telephone which reproduces the sound to the receiving user. The term is derived from Greek: τῆλε tēle, far & φωνή phōnē, voice, together meaning distant voice. A common short construct of the term is phone, which came into ownership almost immediately after the number one patent was issued.

In 1876, Alexander Graham Bell was the number one to be granted a United States patent for a device that submission clearly intelligible replication of the human voice at adevice. This instrument was further developed by many others, and became rapidly indispensable in business, government, and in households.

The fundamental elements of a telephone are a announce an incoming telephone call, and a dial or keypad to enter a telephone number when initiating a so-called to another telephone. The receiver and transmitter are ordinarily built into a handset which is held up to the ear and mouth during conversation. The dial may be located either on the handset or on a base segment to which the handset is connected. The transmitter converts the sound waves to electrical signals which are referenced through a telephone network to the receiving telephone, which converts the signals into audible sound in the receiver or sometimes a loudspeaker. Telephones are duplex devices, meaning they permit transmission in both directions simultaneously.

The first telephones were directly connected to each other from one customer's multiple or residence to another customer's location. Being impractical beyond just a few customers, these systems were quickly replaced by manually operated centrally located switchboards. These exchanges were soon connected together, eventually forming an automated, worldwide public switched telephone network. For greater mobility, various radio systems were developed for transmission between mobile stations on ships and automobiles in the mid-20th century. Hand-held mobile phones were featured for personal improvement starting in 1973. In later decades, their analog cellular system evolved into digital networks with greater capability and lower cost.

Convergence has given most contemporary cell phones capabilities far beyond simple voice conversation. almost are smartphones, integrating any mobile communication and many computing needs.

Early commercial instruments

Early telephones were technically diverse. Some used a water microphone, some had a metal diaphragm that induced current in an electromagnet wound around a permanent magnet, and some were dynamic – their diaphragm vibrated a coil of wire in the field of a permanent magnet or the coil vibrated the diaphragm. The sound-powered dynamic variants survived in small numbers through the 20th century in military and maritime applications, where its ability to create its own electrical energy was crucial. Most, however, used the Edison/Berliner carbon transmitter, which was much louder than the other kinds, even though it requested an induction coil which was an impedance matching transformer to make it compatible with the impedance of the line. The Edison patents kept the Bell monopoly viable into the 20th century, by which time the network was more important than the instrument.

Early telephones were locally powered, using either a dynamic transmitter or by the powering of a transmitter with a local battery. One of the jobs of outside plant personnel was to visit used to refer to every one of two or more people or things telephone periodically to inspect the battery. During the 20th century, telephones powered from the telephone exchange over the same wires that carried the voice signals became common.

Early telephones used a single wire for the subscriber's line, with ground return used to prepare the circuit as used in telegraphs. The earliest dynamic telephones also had only one port opening for sound, with the user alternately listening and speaking or rather, shouting into the same hole. Sometimes the instruments were operated in pairs at each end, creating conversation more convenient but also more expensive.

At first, the benefits of a telephone exchange were not exploited. Instead, telephones were leased in pairs to a subscriber, who had to arrange for a telegraph contractor to construct a quality between them, for example between a home and a shop. Users who wanted the ability to speak to several different locations would need to obtain and ready three or four pairs of telephones. Western Union, already using telegraph exchanges, quickly extended the principle to its telephones in New York City and San Francisco, and Bell was not late in appreciating the potential.

Signalling began in an appropriately primitive manner. The user alerted the other end, or the exchange operator, by whistling into the transmitter. Exchange operation soon resulted in telephones being equipped with a bell in a ringer box, first operated over awire, and later over the same wire, but with a condenser capacitor in series with the bell coil to permit the AC ringerthrough while still blocking DC keeping the phone "on hook". Telephones connected to the earliest Strowger switch automatic exchanges had seven wires, one for the knife switch, one for each telegraph key, one for the bell, one for the push-button and two for speaking. Large wall telephones in the early 20th century commonly incorporated the bell, and separate bell boxes for desk phones dwindled away in the middle of the century.

Rural and other telephones that were not on a common battery exchange had a magneto hand-cranked generator to produce a high voltage alternatingto ring the bells of other telephones on the rank and to alert the operator. Some local farming communities that were not connected to the leading networks set up barbed wire telephone lines that exploited the existing system of field fences to transmit the signal.

In the 1890s a new smaller style of telephone was introduced, packaged in three parts. The transmitter stood on a stand, known as a "candlestick" for its shape. When not in use, the receiver hung on a hook with a switch in it, known as a "switchhook". previous telephones required the user to operate a separate switch to connect either the voice or the bell. With the new kind, the user was less likely to leave the phone "off the hook". In phones connected to magneto exchanges, the bell, induction coil, battery and magneto were in a separate bell box or "ringer box". In phones connected to common battery exchanges, the ringer box was installed under a desk, or other out-of-the-way place, since it did not need a battery or magneto.

Cradle designs were also used at this time, having a handle with the receiver and transmitter attached, now called a handset, separate from the cradle base that housed the magneto crank and other parts. They were larger than the "candlestick" and more popular.

Disadvantages of single-wire operation such(a) as crosstalk and hum from nearby AC power to direct or introducing wires had already led to the use of twisted pairs and, for long-distance telephones, four-wire circuits. Users at the beginning of the 20th century did not place long-distance calls from their own telephones but made an appointment to use a special soundproofed long-distance telephone booth furnished with the latest technology.

What turned out to be the most popular and longest-lasting physical style of telephone was introduced in the early 20th century, including Bell's 202-type desk set. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use sat in a cradle in the base unit. The circuit diagram of the benefit example 202 shows the direct association of the transmitter to the line, while the receiver was induction coupled. In local battery configurations, when the local loop was too long to provide sufficient current from the exchange, the transmitter was powered by a local battery and inductively coupld, while the receiver was included in the local loop. The coupling transformer and the ringer were mounted in a separate enclosure, called the subscriber set. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1 to 10 times for each digit, and the hook switch in the center of the circuit diagram disconnected the line and the transmitter battery while the handset was on the cradle.