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Wednesday, 29 June 2011

Telephone prehistory

Telephone prehistory

Mechanical devices

Before the invention of electromagnetic telephones, there were mechanical devices for transmitting spoken words over a greater distance than that of normal speech. The very earliest mechanical telephones were based on sound transmission through pipes or other physical media. Speaking tubes long remained common, including a lengthy history of use aboard ships, and can still be found today.

19th century 'tin can', or 'lover's' telephone
A different device, the tin can telephone, or 'lover's phone', has also been known for centuries. It connected two diaphragms with a taut string or wire, which transmitted sound by mechanical vibrations from one to the other along the wire, and not by a modulated electrical current. The classic example is the children's toy made by connecting the bottoms of two paper cups, metal cans, or plastic bottles with string.

Electrical devices

The telephone emerged from the creation of, and successive improvements to the electrical telegraph. In 1804 Catalan polymath and scientist Francisco Salvá i Campillo constructed an electrochemical telegraph.[1] An electromagnetic telegraph was created by Baron Schilling in 1832. Carl Friedrich Gauß and Wilhelm Weber built another electromagnetic telegraph in 1833 in Göttingen.

The electrical telegraph built and owned by Samuel F. B. Morse
The first commercial electrical telegraph was constructed by Sir William Fothergill Cooke and entered use on the Great Western Railway in England. It ran for 13 miles from Paddington station to West Drayton and came into operation on April 9, 1839.
Another electrical telegraph was independently developed and patented in the United States in 1837 by Samuel Morse. His assistant, Alfred Vail, developed the Morse code signaling alphabet with Morse. America's first telegram was sent by Morse on January 6, 1838, across two miles of wiring.
During the second half of the 19th century inventors tried to find ways of sending multiple telegraph messages simultaneously over a single telegraph wire by using different modulated audio frequencies for each message. These inventors included Charles Bourseul, Thomas Edison, Elisha Gray, and Alexander Graham Bell. Their efforts to develop acoustic telegraphy in order to significantly reduce the cost of telegraph messages led directly to the invention of the telephone, or 'the speaking telegraph'.

Invention of the telephone

Invention of the telephone

Credit for the invention of the electric telephone is frequently disputed, and new controversies over the issue have arisen from time-to-time. Charles Bourseul, Antonio Meucci, Johann Philipp Reis, 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 mass of lawsuits to resolve the patent claims of 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.
  • Alexander Graham Bell has most often been credited as the inventor of the first practical telephone. Additionally, 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. In Germany, Johann Philipp Reis is seen as a leading telephone pioneer who stopped only just short of a successful device. However, the modern telephone is the result of work done by many people, all worthy of recognition of their contributions to the field. Bell was, however, the first to patent the telephone, an "apparatus for transmitting vocal or other sounds telegraphically".

20th Century developments

20th Century developments

Old Receiver schematic, c.1906
A German rotary telephone, the W48
Top of cellular telephone tower
By 1904 there were over three million phones in the US,[4] still connected by manual switchboard exchanges. By 1914, the U.S. was the world leader in teledensity and had more than twice the teledensity of Sweden, New Zealand, Switzerland, and Norway. The relative good performance of the U.S. occurred despite competing telephone networks not interconnecting.[5]
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 Model 102. 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 Model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled, with energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate enclosure. The dial switch in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1-10 times for each digit, and the hook switch (in the center of the circuit diagram) permanently disconnected the line and the transmitter battery while the handset was on the cradle.
After the 1930s, the base of the telephone also enclosed its bell and induction coil, obviating the old separate ringer box. Power was supplied to each subscriber line by central office batteries instead of the user's local battery which required periodic service. For the next half century, the network behind the telephone grew progressively larger and much more efficient, and after the rotary dial was added the instrument itself changed little until touch-tone signaling started replacing the rotary dial in the 1960s.
The history of mobile phones can be traced back to two-way radios permanently installed in vehicles such as taxicabs, police cruisers, railroad trains, and the like. Later versions such as the so-called transportables or "bag phones" were equipped with a cigarette lighter plug so that they could also be carried, and thus could be used as either mobile two-way radios or as portable phones by being patched into the telephone network.
In December 1947, Bell Labs engineers Douglas H. Ring and W. Rae Young proposed hexagonal cell transmissions for mobile phones.[6] Philip T. Porter, also of Bell Labs, proposed that the cell towers be at the corners of the hexagons rather than the centers and have directional antennas that would transmit/receive in 3 directions (see picture at right) into 3 adjacent hexagon cells.[7] [8] The technology did not exist then and the radio frequencies had not yet been allocated. Cellular technology was undeveloped until the 1960s, when Richard H. Frenkiel and Joel S. Engel of Bell Labs developed the electronics.

Early commercial instruments

Early commercial instruments

The earliest telephones had only one wire for both transmitting and receiving of audio, and used a ground return path, as was found in telegraph systems. The earliest dynamic telephones also had only one opening for sound, and the user alternately listened and spoke (rather, shouted) into the same hole. Sometimes the instruments were operated in pairs at each end, making conversation more convenient but also more expensive.
Historical marker commemorating the first telephone central office in New York State (1878)
At first, the benefits of a switchboard exchange were not exploited. Instead, telephones were leased in pairs to the subscriber, for example one for his home and one for his shop, who must arrange with telegraph contractors to construct a line between them. Users who wanted the ability to speak to three or four different shops, suppliers etc. would obtain and set up 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 slow in appreciating the potential.
Signaling 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, first operated over a second wire and later with the same wire using a condenser. Telephones connected to the earliest Strowger 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.
Rural and other telephones that were not on a common battery exchange had a "magneto" or hand cranked generator to produce a high voltage alternating signal to ring the bells of other telephones on the line and to alert the exchange operator.
In 1877 and 1878, Edison invented and developed the carbon microphone used in all telephones along with the Bell receiver until the 1980s. After protracted patent litigation, a federal court ruled in 1892 that Edison and not Emile Berliner was the inventor of the carbon microphone. The carbon microphone was also used in radio broadcasting and public address work through the 1920s.
1896 Telephone (Sweden)
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 called a "ringer box." [3] 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, 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 as crosstalk and hum from nearby AC power 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 sound proofed long distance telephone booth furnished with the latest technology.

Early telephone developments

Early telephone developments

The following is a brief summary of the history of the development of the telephone:
A French Gower telephone of 1912 at the Musée des Arts et Métiers in Paris
  • 1667: Robert Hooke invented a string telephone that conveyed sounds over an extended wire by mechanical vibrations.
  • 1844: Innocenzo Manzetti first mooted the idea of a “speaking telegraph” (telephone).
  • 1854: Charles Bourseul writes a memorandum on the principles of the telephone.(See the article : "Transmission électrique de la parole", L'Illustration, Paris, 26 August 1854).
  • 1854: Antonio Meucci demonstrates an electric voice-operated device in New York; it is not clear what kind of device he demonstrated.
  • 1861: Philipp Reis constructs the first speech-transmitting telephone
  • December 28, 1871: Antonio Meucci files a patent caveat No. 3353 at the U.S. Patent Office for a device he named "Sound Telegraph".[2]
  • 1872: Elisha Gray establishes Western Electric Manufacturing Company.
  • July 1, 1875: Bell uses a bi-directional "gallows" telephone that was able to transmit "voicelike sounds", but not clear speech. Both the transmitter and the receiver were identical membrane electromagnet instruments.
  • 1875: Thomas Edison experiments with acoustic telegraphy and in November builds an electro-dynamic receiver, but does not exploit it.
  • 1875: Hungarian Tivadar Puskas (the inventor of telephone exchange) arrived in the USA.
  • April 6, 1875: Bell's U.S. Patent 161,739 "Transmitters and Receivers for Electric Telegraphs" is granted. This uses multiple vibrating steel reeds in make-break circuits, and the concept of multiplexed frequencies.
  • January 20, 1876: Bell signs and notarizes his patent application for the telephone.
  • February 11, 1876: Elisha Gray designs a liquid transmitter for use with a telephone, but does not build one.
  • March 7, 1876: Bell's U.S. patent No. 174,465 for the telephone is granted.
  • March 10, 1876: Bell transmits the sentence: "Mr. Watson, come here! I want to see you!" using a liquid transmitter and an electromagnetic receiver.
  • January 30, 1877: Bell's U.S. patent No. 186,787 is granted for an electromagnetic telephone using permanent magnets, iron diaphragms, and a call bell.
  • April 27, 1877: Edison files for a patent on a carbon (graphite) transmitter. Patent No. 474,230 was granted on May 3, 1892, after a 15-year delay because of litigation. Edison was granted patent No. 222,390 for a carbon granules transmitter in 1879.
  • 1877: First long-distance telephone line
  • 1915: First U.S. coast-to-coast long-distance telephone call, ceremoniously inaugurated by A.G. Bell in New York City and his former assistant Thomas Augustus Watson in San Francisco, Californi