Broadcast television systems

Broadcast television systems are encoding or formatting standards for the transmission and reception of terrestrial television signals. There were three main analog television systems in use around the world until late 2010s (expected): NTSC, PAL, and SECAM. Now in digital television (DTV), there are four main systems in use around the world: ATSC, DVB, ISDB and DTMB.

Analog television systems

All but one analog television system began as black-and-white systems. Each country, faced with local political, technical, and economic issues, adopted a color television system which was grafted onto an existing monochrome system, using gaps in the video spectrum (explained below) to allow color transmission information to fit in the existing channels allotted. The grafting of the color transmission standards onto existing monochrome systems permitted existing monochrome television receivers predating the changeover to color television to continue to be operated as monochrome television. Because of this compatibility requirement, color standards added a second signal to the basic monochrome signal, which carries the color information. The color information is called chrominance with the symbol C, while the black and white information is called the luminance with the symbol Y. Monochrome television receivers only display the luminance, while color receivers process both signals. Though in theory any monochrome system could be adopted to a color system, in practice some of the original monochrome systems proved impractical to adapt to color and were abandoned when the switch to color broadcasting was made. All countries used one of three color systems: NTSC, PAL, or SECAM.

Terrestrial television

Terrestrial television or broadcast television is a type of television broadcasting in which the television signal is transmitted by radio waves to the TV receiver from a terrestrial (Earth based) transmitter, a television station, and received with an antenna. The term is more common in Europe, while in North America it is referred to as broadcast television or sometimes over-the-air television (OTA). The term "terrestrial" is used to distinguish this type from the newer technologies of satellite television (direct broadcast satellite or DBS television), in which the television signal is transmitted to the receiver from an overhead satellite, and cable television, in which the signal is carried to the receiver through a cable.

Terrestrial television was the first technology used for television broadcasting, with the first long-distance public television broadcast from Washington, D.C., on 7 April 1927. The BBC began broadcasting in 1929, and had a regular schedule of television programmes in 1930. However these early experimental systems had insufficient picture quality to attract the public, due to their mechanical scan technology, and television didn't become widespread until after World War 2 with the advent of electronic scan technology. The television broadcasting business followed the model of radio networks, with local television stations in cities and towns affiliated with television networks, either commercial (in USA) or government-controlled (in Europe), which provided content. Television broadcasts were in black and white until the 1960s, when color television broadcasting began.