Cable television began with antennas on hilltops feeding towns that mountains cut off
In 1948, rural American communities hidden behind hills could barely pull in a television picture. The fix was blunt: raise one enormous antenna on high ground, taller than anyone could afford alone, and run coaxial cable from it straight into every house. That shared community antenna grew into cable television, eventually reaching most American homes.
Local cable networks had appeared even earlier in Europe. In 1936 Rediffusion ran one in London, and Berlin had another that year, notably for the Olympic Games. These early systems simply caught weak broadcast signals, boosted them and passed them along unshielded wires. In the United States cable became a commercial business in the 1950s, serving small towns with no stations of their own. Canada was different: towns that had perfectly good local signals still signed up, because viewers wanted American channels.
Early sets had twelve channel numbers, yet a single city could use only seven, because receivers of the day distorted strong local signals sitting on neighbouring channels. Cable engineers squeezed in more by using so-called midband and superband frequencies, reachable at first only with a separate tuner box. Early pay services such as HBO rode on those odd frequencies unscrambled, since ordinary televisions could not tune them anyway. Once sets could receive all 181 channels the regulator allotted, premium services had to scramble, and hobby magazines like Popular Electronics promptly printed circuits for building your own descrambler.
Uptake climbed steeply. In 1968 about 6.4 percent of American households had cable; by 1988 the figure was 52.8 percent, and by 1994 it reached 62.4 percent. The same wires now also carry FM radio, internet access and telephone service.
Many channels share one cable through a trick called frequency division multiplexing: at the central headend each channel is shifted to its own frequency slot so the signals never collide, and the set-top box shifts the chosen one back for display. Modern systems send signals most of the way over optical fibre, converting them to electrical form at neighbourhood nodes. Since digital channels are now encrypted to curb theft, each television generally needs its own box.
Source: Cable television
