| 摘要 |
PURPOSE:To operate the transistor always at best cindition, which is operated as a mixer in case of VHF reception and is operated as IF amplifier at UHF reception, by providing diode. CONSTITUTION:At VHF reception, the selector switch S is selected to a position, and the television signal from the terminal 1 is inputted to TR11 in which the transistor TR11 is set at efficient operating point as a mixer consisting of the resistors 16,17 and the emitter resistor. On the other hand, at UHF reception, the switch S is set to position b, and the intermediate frequency signal of UHF tuner 22 passes through the resistor 31 and it is fed to TR 11 via the diode 32. With this constitution, at VHF reception, the diode 32 is non-conductive because the cathode is back biased with the bias of TR11, and TR11 can be operated at best condition as a mixer. Further, at UHF reception, the diode 32 is conductive, and TR11 can be operated at best condition as IF amplifier by suitably setting the resistor 31. |
