Radio Broadcast Receiver

a radio receiver designed for the reception and acoustic reproduction of sound-broadcasting programs. Radio broadcast receivers manufactured in the USSR are used to receive long-wave, medium-wave, shortwave, and ultrashort wave signals. They can receive amplitude-modulated (AM) signals transmitted by broadcast stations in the frequency ranges from 150 to 405 kilohertz (kHz) (2,000–740.7 m), from 525 to 1,605 kHz (571.4–186.9 m), and from 3.95 to 12.1 megahertz (MHz) (75.9–24.8 m). They can receive frequency-modulated signals in the range from 66.0 to 74.0 MHz (4.55–4.06 m). The limits of the standard frequency bands for radio broadcasting are different in different countries and do not coincide with the limits used, for example, in radio communication or radio physics.

In the USSR, radio broadcast receivers are divided into several classes according to their basic characteristics, frequency ranges, and convenience of use. The three main types are nonportable (including stereophonic very-high-frequency receivers), portable, and automobile receivers. A radio broadcast receiver is often structurally combined with a record player in a radio-phonograph, with a tape recorder in a radio-tape recorder, or with both in a radio-tape recorder-phonograph.

Most radio broadcast receivers in use in the mid 1970’s are of the superheterodyne type. In these receivers, semiconductor devices, including integrated microcircuits, or, more rarely, electron tubes are used for signal amplification, frequency conversion, and detection. The principal amplification (about 10⁴ times) of the desired signal is obtained in what is called an intermediate-frequency amplifier. Voltage and power amplification of the detected oscillations is accomplished by the stages of a low-frequency (audio) amplifier in which provision is made for volume control and treble-and-bass control. The oscillations, now increased in power, are fed to an acoustic system consisting of one or more loudspeakers.

The tuning of a radio broadcast receiver to a particular station consists first of all in the selection, by switching to the appropriate receiver circuits, of the frequency band that contains the station’s carrier frequency. Then, by manual adjustment, the station indicator is set at the point on the dial or scale corresponding to the carrier frequency or wavelength of the station. This is accomplished by turning the rotor of a gang tuning capacitor or, in automobile receivers, by moving the cores of inductance coils. As a result, the natural resonant frequencies of the input and heterodyne resonant circuits change. In present-day receivers, electronic tuning by means of voltage-variable capacitors has largely supplanted mechanical tuning.