a set of devices for establishing two-way radio communication between several points. Such devices are used in receiving and transmitting telegrams and facsimile images, in conducting telephone conversations, in providing low-level radio communication and the remote control of systems and mechanisms, and in other areas. The basic components of a radio transmitter-receiver include an antenna, a radio transmitter and a radio receiver, a feeder that connects the transmitter and receiver to the antenna, and an electric-power supply.
Radio transmitter-receivers are classified according to their wavelength bands into kilometer wave, hectometer wave, and other radio sets; according to the number of communication channels into single-, two-, or multi-channel sets; according to the mode of operation into simplex or duplex sets; and according to the degree of mobility into portable, vehicular, and stationary sets. The operating range is basically determined by the power of the transmitter, by the sensitivity of the receiver, by the directivity of the antenna, by the type of modulation and demodulation, and by conditions affecting the propagation of radio waves.
Portable radio transmitter-receivers are compact and weigh from several grams to 20 kg. They operate in the meter or decimeter wavelength range, have a transmitter power of 0.1–1 watt (W), and provide communication over a range of several tens of km. In transistorized portable units, the transmitter and receiver, as a rule, have an integrated construction, the same antenna, and several common functional modules (the transceiver format). A storage battery usually serves as the power source; the use of primary batteries or hand generators is less frequent.
Radio transmitter-receivers installed in automobiles, aircraft, tanks, ships, and spacecraft generally have structurally separated receivers and transmitters. Such sets are equipped with several different types of antennas for duplex operation on various wavelengths. They operate in the meter and decimeter wave bands. With transmitter output powers of approximately 10-1-103 W or more, they provide communication over distances of several hundred km. Their power can be supplied by a storage battery, a solar battery (in spacecraft), a built-in power-supply unit, or an onboard power system.
Stationary radio transmitter-receivers, such as those used in the stations of a radio-relay system or in amateur radio communications, also have separate transmitters and receivers operating with one or several antennas. With transmitter powers of 10-1 -102 W, they provide a communication range of several tens of km at superhigh frequencies. At decameter wavelengths, their operating range makes it possible to establish communications with practically any point on earth.
V. V. IGNATOV and A. P. RODIMOV