Open wire was an early

transmission Transmission may refer to: Medicine, science and technology * Power transmission ** Electric power transmission ** Propulsion transmission, technology allowing controlled application of power *** Automatic transmission *** Manual transmission *** ...

technology in

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

, first used in

telegraphy Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...

. It consisted of pairs of electric wire strung on a pole line between communities, towns, and cities. The wire of the

transmission line In electrical engineering, a transmission line is a specialized cable or other structure designed to conduct electromagnetic waves in a contained manner. The term applies when the conductors are long enough that the wave nature of the transmis ...

was attached to the cross-arms of each pole with glass insulators.E.F. O'Neill (ed.), Bell Telephone Laboratories Staff,, ''A History of Engineering and Science in the Bell System–Transmission Technology (1925–1975)'' AT&T Bell Laboratories (1985), ISBN 0-932764-08-8, p.4 It was originally manufactured from iron or steel, but developments in annealing of

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

made it possible to use this metal by the 1890s to reduce

electrical resistance The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares some conceptual parallels ...

substantially. Copper wire was drawn to a diameter of up to 1/6 inch (165 mils). The glass insulators on the pole cross-arms were spaced at about 12 inches apart. Typically up to five wire pairs were installed on each crossarm, and multiple cross-arms could be installed on each pole. The practical limit in distance of

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

communication via open-wire transmission was reached when the

Bell System The Bell System was a system of telecommunication companies, led by the Bell Telephone Company and later by the American Telephone and Telegraph Company (AT&T), that dominated the telephone services industry in North America for over one hundr ...

long-distance network was extended from New York City to Denver in 1911. Despite heavy-gauge wire, and using

loading coil A loading coil or load coil is an inductor that is inserted into an electronic circuit to increase its inductance. The term originated in the 19th century for inductors used to prevent signal distortion in long-distance telegraph transmission c ...

s to reduce transmission loss, talking was just barely possible over the line.

References

*Chapman, A.G. ''Open-Wire Crosstalk'', BSTJ 13(1)19, January 1934 *B.C. Griffith, H. Kahl, ''Type-O Carrier System Objectives'' BLR 32(6)p209 (June 1954) {{refend Communication circuits Telecommunications techniques Telephony equipment Telephony Transmission lines

See also

References