History

History

Main articles: History of the telephone and Timeline of the telephone

Further information: Invention of the telephone, Elisha Gray and Alexander Bell telephone controversy, and Canadian Parliamentary Motion on Alexander Graham Bell

Bell placing the first New York to Chicago telephone call in 1892

Credit for the invention of the electric telephone is frequently disputed, and new controversies over the issue have arisen from time to time. As with other influential inventions such as radio, television, the light bulb, and the computer, there were several inventors who did pioneering experimental work on voice transmission over a wire and improved on each other's ideas. Innocenzo Manzetti, Antonio Meucci, Johann Philipp Reis, Elisha Gray, Alexander Graham Bell, and Thomas Edison, among others, have all been credited with pioneering work on the telephone. An undisputed fact is that Alexander Graham Bell was the first to be awarded a patent for the electric telephone by theUnited States Patent and Trademark Office (USPTO) in March 1876.^[2] That first patent by Bell was the master patent of the telephone, from which other patents for electric telephone devices and features flowed.^[3]

The early history of the telephone became and still remains a confusing morass of claims and counterclaims, which were not clarified by the large number of lawsuits that hoped to resolve the patent claims of many individuals and commercial competitors. The Bell and Edison patents, however, were forensically victorious and commercially decisive.

In 1876, shortly after the telephone was invented, Hungarian engineer Tivadar Puskás invented the telephone switchboard which allowed for the formation of telephone exchanges, and eventually networks.^[4]

Basic principles

Schematic of a landline telephone installation.

A traditional landline telephone system, also known as "plain old telephone service" (POTS), commonly carries both control and audio signals on the same twisted pair (C) of insulated wires: the telephone line. The signaling equipment, or ringer, (see figure left) consists of a bell, beeper, light or other device (A7) to alert the user to incoming calls, and number buttons or a rotary dial (A4) to enter a telephone number for outgoing calls. Most of the expense of wire-line telephone service is the wires, so telephones transmit both the incoming and outgoing voice channels on a single pair of wires. A twisted pair line rejects electromagnetic interference (EMI) and crosstalk better than a single wire or an untwisted pair. The strong outgoing voice signal from the microphone does not overpower the weaker incoming speaker signal with a sidetone because a hybrid coil (A3) subtracts the microphone's signal from the signal sent to the local speaker. The junction box (B) arrests lightning (B2) and adjusts the line's resistance (B1) to maximize the signal power for the line's length. Telephones have similar adjustments for inside line lengths (A8). The wire's voltages are negative compared to earth, to reduce galvanic corrosion. Negative voltage attracts positive metal ions toward the wires.