Television-Receiver Tuner

the input unit of a television receiver that makes possible the selection of the communications channel carrying a program of interest to the viewer, the discrimination of the radio-frequency signal corresponding to that channel, the amplification of the signal, and the conversion of the signal to an intermediate-frequency signal. Such a tuner is usually manufactured as a separate packaged unit. In addition to a drum or wafer switch, the tuner includes an input circuit, an amplifier, and a converter, which contain resonant circuits (oscillatory circuits or coaxial cavities).

Tuners are produced for the meter band, the decimeter band, or both. In meter-band tuners, channels are changed by switching the inductors in the resonant circuits. Fine-tuning of the local oscillator of the converter is carried out by means of a variable capacitor. In decimeter-band tuners, these operations are accomplished by continuous tuning of the resonant frequency of the coaxial cavities.

The use of electronically controlled tuners began in the 1970’s. In such tuners the selection of channels is carried out by means of switching semiconductor diodes. The resonant circuits are tuned through the use of varicaps (varactors). The control devices of such tuners are of the push-button type or of the sensor (touch-operated) type.