| 摘要 |
PURPOSE:To improve the isolation between the UHF and VHF parts in a simple constitution, by connecting between the mixture terminal and the cathode terminal of the high frequency switch diode via the resistance. CONSTITUTION:Mixer terminal 20 is connected to the cathode terminal of high frequency switch diode 11 via resistance 31. Thus diode 11 of the input circuit receives the backward bias at all times to secure the OFF mode at the time of receiving the VHF low band as well as the UHF and by the +B voltage supplied to the mixer terminal. Accordingly, the low band receiving mode is secured by supplying the +B voltage to terminal 19, and no disturbance due to the nonlinear distortion of diode 11 is caused in the UHF receiving mode under which the +B voltage is supplied to terminal 19. On the other hand, the +B voltage is applied to terminal 21 at the time of the receiving the VHF high band to give the forward bias to diode 11. In such way, the isolation can be improved between the UHF and VHF parts in a simple constitution. |
