coaxial cable
Coaxial cable is the kind of copper cable used by cable TV companies
between the community antenna and user homes and businesses. Coaxial cable
is sometimes used by telephone companies from their central office to the
telephone poles near users. It is also widely installed for use in business
and corporation Ethernet and other types of
local area network.
Coaxial cable is called "coaxial" because it includes one physical
channel that carries the signal surrounded (after a layer of insulation)
by another concentric physical channel, both running along the same axis.
The outer channel serves as a ground. Many of these cables or pairs of
coaxial tubes can be placed in a single outer sheathing and, with repeaters,
can carry information for a great distance.
Coaxial cable was invented in 1929 and first used commercially in 1941.
AT&T established its first cross-continental coaxial transmission system
in 1940. Depending on the carrier technology used and other factors, twisted
pair copper wire and optical fiber are alternatives
to coaxial cable.