Telecommunicatio

Satellite Telephone

A telephone company employee displays a handset used in the firm's satellite telephone system. Satellite telephones enable direct communications to telephone networks from anywhere on the globe. Users can also communicate even if no wired or cellular telephone network exists.

Early Telephones

While working on sound transmission for the deaf, Alexander Graham Bell discovered that steady electric current can be altered to resemble the vibrations made by the human voice. In 1876 he patented a device that sent speech along wires and called it the telephone. Early models of the telephone include Edison’s 1879 wall-mounted phone (left), the candlestick design common in the 1920s and 1930s (bottom), and a 1937 “cradle” telephone, a style popular since 1890 (shown right).

Alexander Graham Bell's Telephone

Alexander Graham Bell constructed this prototype telephone in 1875. The device consists of a coil of wire, a magnetic arm and a taut membrane. Any sound causes the membrane, and hence the magnetic arm, to vibrate. The movement of the magnet induces a fluctuating electric current in the coil. This electrical signal can be reconverted into sound by an identical apparatus at the other end of the circuit.

Alexander Graham Bell

Alexander Graham Bell’s attempts to electrically transmit speech resulted in a patent for the telephone in 1876. Bell founded the Bell Telephone Company to manufacture telephones and operate the telephone network. Bell’s company, later known as AT&T Corp., grew to dominate the telecommunications industry until a 1984 antitrust suit divested the company of its local telephone networks.

Fiber-Optic Strands

A strand of fiber-optic cable reflects the light that passes through it back into the fiber, so light cannot escape the strand. Fiber-optic cables carry more information, suffer less interference, and require fewer signal repeaters over long distances than wires.

Cellular Telephone

Portable cellular telephones have become an invaluable tool for people who need to stay in touch while on the move. Cellular telephone systems combine radio and television technology with computer systems. As a caller moves from one geographical cell (the name given to a specific part of the area being covered by the system) to another, computers in switching offices transfer calls among variously located antenna transmitters without interrupting service.