| 摘要 |
PURPOSE:To realize the isolation between transmission and reception with a simple constitution by providing a power-down function to an amplifier which amplifies the output of a synthesizer up to a drive level or a reception local level of a transmission power amplifier. CONSTITUTION:An amplifier 12 varies the power supply voltage supplied to an amplifier 14 between the transmission and reception modes via a transistor TR1, a switching circuit consisting of resistances R2 and R3 and a resistance R1. Thus the output of the amplifier is varied. When a press switch 15 is turned on, a current flows through resistances R2 and R3 to turn on the TR1. Then the power supply voltage is applied to the amplifier 14, and the output of the amplifier 12 delivers the drive level of a transmission power amplifier 4. While the TR1 is turned off when the switch 15 is off and in a reception state. Then the voltage lower than the power supply voltage by an amount equal to the voltage drop of the R1 is supplied to the amplifier 14. Therefore the output level of the amplifier 12 is reduced compared with the level set in a transmission mode. |
