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television network[′tel·ə‚vizh·ən ‚net‚wərk]
a complex of technical facilities designed for television broadcasting. The principal elements in a television network are the television stations and connecting communications lines, which provide the television channels, radio-relay communications links, cable links, and satellite communications links.
Because of the characteristics of radio-wave propagation in the very-high-frequency (VHF) and ultrahigh-frequency (UHF) bands used for television broadcasting, the transmitting radius of a television station depends on the line-of-sight distance between the transmitting and receiving antennas, which is a function of the height of the antennas above the earth’s surface. The power of a television transmitter determines only the signal strength within the area of line of sight. Transmitting antennas are therefore mounted on high supports. The standard supports used in the USSR television network are 200 and 350 m high, and the standard transmitter output is 5 or 50 kilowatts; this yields good signal reception within a radius of 60 to 80 km.
In order to provide television reception over large areas, a considerable number of transmitting stations separated from one another by no more than 100 to 150 km are needed. However, mutual interference between transmitting stations operating on the same frequencies may occur as a result of the anomalous longdistance propagation of radio waves; such interference may be avoided if the distance between transmitters is no less than 350 to 400 km.
As of 1975, the USSR television network comprised 130 television centers, approximately 1,800 television transmitting stations, more than 100,000 km of long-distance land communications links, and a space communications system using Molniia communications satellites and approximately 70 Orbita receiving stations. The network provides television reception for more than three-fourths of the country’s population.
During the network’s initial development period, principal efforts were devoted to the construction of television centers capable of producing their own programs and equipped with their own powerful transmitting stations. Such centers were constructed in the capitals of the Union and autonomous republics and in cities in the densely populated industrial areas located at considerable distances from one another. These centers are still used for broadcasting local television programs. By the mid-1970’s, construction was limited to television transmitting stations, which obtained their programs from long-distance television communications links. In the period 1965–75, the individual local networks of the USSR were united by land and space communications links into a single television network that provides for the nationwide transmission of programs from Central Television. On Apr. 14, 1961, the USSR network was linked with the Eurovision network; the inaugural program was a broadcast of a reception for Iu. A. Gagarin in Moscow.
The network makes extensive use of low-power (1–100 watts) repeater stations with an operating radius of 2 to 15 km. These are ordinarily located at intermediate points in radio-relay and cable links to provide television transmissions for individual small areas and settlements. They can be located beyond the range where good reception of the main transmitting stations by home television receivers is not possible, thus extending the operating range of the main stations. Repeaters located at elevations where the signal strength from the station being retransmitted is high can establish normal reception in shadow regions located within the rated operating radius of a transmitter; such shadow regions occur where terrain features block reception of the main station, for example, in settlements located in low spots and especially in mountainous valleys.
Cable television systems are also part of the television network. They range from the simplest types, which consist of a master antenna that feeds signals by cable to television receivers in individual houses or apartment groups within a building, to complicated, branched systems that serve several thousand subscribers. Cable systems can be used to extend the operating radius of main television transmitters. They are practically the only means of providing normal reception conditions in shadow regions that exist in certain city districts. Such shadow regions are caused by houses of different heights constructed close together—a typical situation in modern cities.
REFERENCESShliuger, I. S. “Postroenie televizionnykh setei na ravninnoi i gornoi mestnosti.” Elektrosviaz’, 1972, no. 7.
Krivosheev, M. I. Perspektivy razvitiia televideniia. Moscow, 1972.
Varbanskii, A. M. “Sostoianie i napravleniia dal’neishego razvitiia peredaiushchei televizionnoi seti SSSR.” Elektrosviaz’, 1975, no. 9.
A. M. VARBANSKII