<P> In the United States and some other countries, cable television distribution systems use extensive networks of outdoor coaxial cable, often with in - line distribution amplifiers . Leakage of signals into and out of cable TV systems can cause interference to cable subscribers and to over-the - air radio services using the same frequencies as those of the cable system . </P> <Ul> <Li> 1880--Coaxial cable patented in England by Oliver Heaviside, patent no . 1,407 . </Li> <Li> 1884--Siemens & Halske patent coaxial cable in Germany (Patent No. 28,978, 27 March 1884). </Li> <Li> 1929--First modern coaxial cable patented by Lloyd Espenschied and Herman Affel of AT&T's Bell Telephone Laboratories . </Li> <Li> 1936--First closed circuit transmission of TV pictures on coaxial cable, from the 1936 Summer Olympics in Berlin to Leipzig . </Li> <Li> 1936--World's first underwater coaxial cable installed between Apollo Bay, near Melbourne, Australia, and Stanley, Tasmania . The 300 km cable can carry one 8.5 - kHz broadcast channel and seven telephone channels . </Li> <Li> 1936--AT&T installs experimental coaxial telephone and television cable between New York and Philadelphia, with automatic booster stations every ten miles . Completed in December, it can transmit 240 telephone calls simultaneously . </Li> <Li> 1936--Coaxial cable laid by the General Post Office (now BT) between London and Birmingham, providing 40 telephone channels . </Li> <Li> 1941--First commercial use in USA by AT&T, between Minneapolis, Minnesota and Stevens Point, Wisconsin . L1 system with capacity of one TV channel or 480 telephone circuits . </Li> <Li> 1949--On January 11, eight stations on the US East Coast and seven Midwestern stations are linked via a long - distance coaxial cable . </Li> <Li> 1956--First transatlantic coaxial cable laid, TAT - 1 . </Li> </Ul> <Li> 1880--Coaxial cable patented in England by Oliver Heaviside, patent no . 1,407 . </Li> <Li> 1884--Siemens & Halske patent coaxial cable in Germany (Patent No. 28,978, 27 March 1884). </Li>

Why most coaxial cables have a characteristic impedance of either 50 ohms or 75 ohms