| 摘要 |
PURPOSE:To realize antenna turning in the best state automatically without the need of reducing the Q of the antenna by constituting a variable condenser of an antenna tuning circuit with a varactor diode and controlling the condenser with a signal from a PLL local oscillation circuit. CONSTITUTION:A signal of a frequency component different from a desired frequency corresponding to a digital signal of a signal line 17 by just an intermediate frequency is outputted from a signal line 15 and a voltage corresponding to the frequency of the line 15 is generated in the line 9. Since a varactor diode is used for a VCO 61 to vary the oscillated frequency, the circuit has only to be controlled by taking the case into account in such a way that the voltage of the line 9 is higher when the frequency of the line 15 is high and when the frequency is low, the voltage is lower. That is, the voltage of the line 9 is amplified properly by a buffer amplifier 7 and given to the varactor diode 111, then an optimum tuning condenser is obtained from the diode 111. Thus, the voltage from a PLL local oscillator 6 is given to the diode 111 to obtain a condensor in response to each radio frequency. |
