Helen Lambourne, age 13, of Baltimore, Md., foher question:
WHAT EXACTLY IS A COAXIAL CABLE?
A coaxial cable is an electrical conduct that is used to transmit long distance telephone calls. It is alsoed to transmit coded, typed or handwritten information as wells facsimile or electronic copy such as maps, pictures and charts.
Coaxial cables can also be use to transmit television programs but most TV is sent by radio relay these days. A coaxial cable is made upf from eight to 20 coaxials. A coaxial consists of a copper tube with copper wire held in the tube's center by plastic insulators. The tube is three eighths of an inch in diameter and the insulators are spaced about one inch apart along the tube.
The tube and wire are the same axis or center and are therefore called coaxial. The tube shields the signal from outside electronic. interference and prevents the signal from losing its strength. The coaxial is wrapped with steel tape for strength, protection and electrical s fielding.
The cable includes several insulated wires as well as the coaxials. The wires are used for control and maintenance. The cable is wrapped in a plastic and lead sheath.
An eight tube cable is about two inches in diameter and a 20 tube cable is about three inches in diameter.
Electronic signals are sensitive to changing temperatures, so most coaxial cables are buried in the earth, which has a more constant temperature. Amplifiers that strengthen the signals may be placed as close as two miles apart.
Coaxials work in pairs. One coaxial carries signals in one direction while the other handles signals in the other direction. One pair of tubes in each cable is usually reserved for use in case of damage to another pair.
Today, a pair of coaxials can carry 3,600 separate signals at the same time. That means that a fully equipped, 20 tube cable, with a pair of tubes in reserve, can carry 32,400 two way conversations simultaneously.
Lloyd Espenshied and Herman Affel, two Bell Telephone engineers, invented the coaxial cable. The cable was successfully tested in 1936.
A coaxial cable was first used commercially in 1941. It provided telephone service between Stevens Point, Wis., and Minnneapolis, Minn. The cable had only four coaxial tubes and provided 480 two way telephone circuits.
Undersea cables lie on the ocean floor. Almost all long distance undersea cables in use today are coaxial. A protective jute or plastic jacket forms the cable's outer layer.
The first transatlantic telephone cable was laid in 1956. It stretched 2,250 miles from Clarenville, Newfoundland, to Oban, Scotland.