ABSTIMMVORRICHTUNG FUER FERNSEHEMPFAENGER

摘要

A tuning apparatus is disclosed in which a television signal of either the UHF band or the VHF band is subjected to frequency conversion to obtain an intermediate frequency and, thereby, the television signal for a desired channel is selected. The tuning apparatus allows either the television signal of the UHF band or the television signal of the VHF band to be converted to an intermediate frequency by means of a common mixer. The mixer is constituted of a balanced mixer of a two-pair differential type. The tuning apparatus includes a local oscillator for reception of the UHF band and a local oscillator for reception of the VHF band. The intermediate frequency stage as the output of the mixer is provided with an attenuator of which the degree of attenuation when the UHF band is received and that when the VHF band is received are different and, thereby, the gains of the apparatus as a whole are equal when receiving the UHF band and when receiving the VHF band. Deterioration in the noise factor is thereby lessened. The RF amplifiers and local oscillators are each provided with a constant current circuit on the emitter side of the amplifying transistor circuit or the oscillator transistor circuit, and the UHF receivable state or the VHF receivable state is brought about by activating or deactivating the constant current circuit. The local oscillation signal is adapted to be supplied to the mixer through amplifiers in two stages and the local oscillation signal for PLL controlling is taken out from the output of the amplifier in the first stage.