| 摘要 |
PURPOSE:To extend the receiving frequency, by constituting a part of the feedback capacity of an oscillating circuit with a varactor diode and connecting an AFC varactor diode to the connection point between tuning coils for high and low bands through specific capacities and applying a tuning voltage to the AFC varactor diode. CONSTITUTION:Varactor diodes CD2-CD4 are provided for oscillating coils L11 and L12 of a local oscillating circuit, and a varactor diode is used as a feedback capacity, thereby extending the oscillation frequency range. Fixed capacities C10 and C11 are inserted in parallel and in series to the varactor diode respectively, and the correction in the high band is performed by the capacity C10, and the correction in the low band is performed by the capacity C11. In respect to an AFC varactor diode DAFC, a capacity CAFC1 of <=1 PF and a capacity CAFC2 of <=10 PF are provided. The capacity CAFC1 determines the AFC control sensitivity in the VHF high band, and the capacity CAFC2 determines the control sensitivity in the VHF low band and the high band. In figure, SWD indicates a switching diode. |
