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television receiver[′tel·ə‚vizh·ən ri‚sē·vər]
a radio receiver designed to amplify and convert the video and audio radio-frequency signals of a television broadcast that have been picked up by a television antenna; the receiver reproduces the visual image broadcast and the accompanying sound. Television receivers are designed for color or black-and-white operation; both nonportable and portable models are produced. Those manufactured in the USSR are capable of receiving signals from television stations transmitting in specifically assigned portions of the very-high-frequency (VHF) band (48.5–100 megahertz and 174–230 megahertz; 12 channels) and ultrahigh-frequency (UHF) band (470–638 megahertz; several tens of channels).
Television receivers must simultaneously amplify and convert video and audio radio-frequency signals. They are usually designed with a superheterodyne circuit, and versions differ in the methods used to extract and amplify the audio signal. The principal components of a television receiver are shown in Figure 1.
The tuner selects the signals of the desired channel and converts them to a lower frequency within the intermediate-frequency passband. The signal-processing circuits include an intermediate-frequency amplifier for the video signal, an amplitude detector, a video amplifier for the brightness signal, and, in color receivers, a color-processing circuit for the chrominance signal. The processing circuit produces a brightness signal and a color-difference signal, which are fed to the control electrodes of a kinescope; an audio signal, which is fed to the audio channel; and horizontal and vertical synchronizing pulses (or a composite television signal), which are fed to a scanning generator. In the color television system used in the USSR, the color-processing circuit for the chrominance signal consists of a band-pass amplifier, in which the chrominance signal is extracted, channels for the direct and delayed signals, an electronic switching device, two frequency detectors for the color-difference signals, a matrix circuit, and amplifiers for the three color-difference signals. The color-processing circuit has provisions for the extraction and decoding of the chrominance signal and for line selection, as well as chrominance disconnect circuits that operate when black-and-white transmissions are received.
The scanning generators include horizontal and vertical scanning circuits that produce sawtooth currents in the horizontal and vertical scanning coils of the deflection system. The high voltage for feeding the second anode of the kinescope (a voltage of 21–25 kilovolts in color receivers) is derived from a special high-voltage winding of the line transformer or by rectifying pulses from the transformer; the voltage for the focusing electrode (approximately 5 kilovolts in a color television set) is similarly derived. In a color receiver, this circuit has transformers to correct pincushion distortion in the television raster.
In order to ensure the dynamic convergence of the beams in a three-beam color kinescope, a convergence circuit is used, in which currents with special wave forms are derived from the horizontal and vertical scanning pulses and are then fed to the windings of the convergence magnets. The convergence magnets are permanent magnets with windings; they provide for the static convergence of the beams. A convergence control unit containing the three convergence magnets is positioned on the neck of the kinescope, as are the blue-corrector and color-purity magnets.
The kinescope’s interface includes static and dynamic white balance controls, switches for extinguishing the electron guns, and regulators for focusing the beams. The demagnetizing circuit for a color kinescope creates a damped alternating current in a demagnetizing loop that circles the kinescope screen. The current demagnetizes the shadow mask and tube rim, which are made of steel.
The audio section consists of an amplifier for the difference frequency, which in the USSR is 6.5 megahertz, a frequency detector for the audio signal, and a low-frequency amplifier from which the audio signal is fed to a high-quality acoustical system, usually composed of several loudspeakers. The power-supply section converts mains voltage into the supply voltages for all components of the television set, including the kinescope and vacuum tube heaters.
In the USSR television receivers are divided into four categories according to quality, screen size, and operating convenience. Categories one to three are nonportable receivers, including both consoles and table models, and class four are portable sets. Receivers are usually designed with subassembly blocks that make extensive use of printed wiring. Semiconductor devices and integrated circuits have supplanted receiving tubes in modern receivers. Development is proceeding on receivers with rectangular screens in the form of flat panels that use phosphors, liquid crystals, or other substances.
Various controls are usually mounted on the front panel of a television receiver. They include an on-off switch, a channel selector, a VHF-UHF switch (when separate channel selectors are provided for each band), and controls for adjusting image brightness, contrast, color saturation, hue, and audio volume and tone. The rear panel usually has a selector for manual or automatic tuning of the local oscillator and a tuning adjustment, a switch for the chrominance channel, and controls for adjusting horizontal and vertical scanning frequencies, for centering the raster, and for adjusting the horizontal and vertical raster linearity and size. Antenna inputs, headphone and tape outputs, and a switch for different power supply voltages are also on the rear panel.
For the viewer’s convenience, the gain, brightness, contrast, local oscillator frequency, horizontal scanning frequency and phase, and image size are regulated automatically. A remote-control transmitter permits the viewer to turn the receiver on and off, change channels, adjust the image brightness and contrast, and control the loudness of the sound from a distance. The transmitter radiates ultrasonic signals that are picked up in the television receiver’s remote-control unit. Signals are fed from the output of the remote-control unit to a control device, which produces control voltages that are fed to various points in the television receiver.
REFERENCESSamoilov, G. P., and V. A. Skotin. Televizory: Al’bom skhem modelei vypuska 1964–1971. Moscow, 1972.
Tsvetnye televizory i ikh ekspluatatsiia. Edited by S. V. Novakovskii. Moscow, 1974.
El’iashkevich, S. A. Televizory. Moscow, 1974.
S. V. NOVAKOVSKII