telecommunications in which telephone messages are transmitted by means of radio waves. In contradistinction to broadcasting, radiotelephone communications provides for a two-way exchange of messages between two correspondents, either simultaneously (duplex communication) or alternately (simplex communication).
In the simplest radiotelephone systems providing either simplex or duplex communications, each correspondent’s radio set consists of a transmitter having a power of 0.1 to 50 watts and using single-side-band or frequency modulation, a sensitive receiver operating in the meter- or decimeter-wavelength ranges, an antenna, a power supply, and a telephone handset. The range of communications may be from 0.5 to 30 km. As a result of their great flexibility and mobility, their low weight, and the simplicity of their maintenance, such systems are used in many areas of the national economy—mostly in low-level communications, including traffic-control communications—and in military services.
In order to provide low-level communications in the sparsely populated regions of the North and Siberia over distances of 300 to 500 km, transmitters are used that have single-side-band modulation in the decameter-wavelength range at powers of 5, 30, and 300 watts. More complicated (usually duplex) radiotelephone systems, such as radio-relay and satellite systems and long-range systems operating at decameter wavelengths, are used to link the telephone systems of various cities and raions in the USSR within the integrated automatic communications system; they use complex directional antennas and powerful single-side-band transmitters of 5 to 100 kilowatts. On long-distance radiotelephone links extending over 5,000 to 6,000 km, the signals are retransmitted by a radio transmitter-receiver located approximately in the middle of the link. At the terminal of a link, each of the link’s telephone channels is coupled to a telephone line, for example, a line to the local automatic telephone exchange.
Unlike multichannel radio-relay and satellite communications systems, long-distance radiotelephone systems operating at decameter wavelengths have few channels (one to four telephone channels); their reliability and intelligibility are poorer, but they are relatively inexpensive and very flexible. These systems are also used for commercial communications with foreign countries, for communications with vessels at sea, and for communications with populated areas in the USSR where radio communications are the only type of telecommunication available.
V. M. ROZOV