| 摘要 |
PURPOSE:To eliminate the need for a trimmer capacitor of an electronic tuning circuit by setting the value of elements used in a local oscillation circuit of the electronic tuning circuit and a tubing circuit of a high frequency amplifier stage or the like within + or -5%. CONSTITUTION:An AM radio wave inputted from an antenna 1 is fed to a high frequency amplifier stage 2 including an antenna tuning circuit or the like. A program signal to tune a desired broadcast wave is fed from a terminal 8 to a PLL circuit 7. The PLL circuit 7 sets the oscillating frequency f0 oscillated from a local oscillation circuit 6 to a prescribed value. A tuning voltage (a) is given to a varactor diode D1 of a high frequency amplifier stage 2 from the PLL circuit 7 and a oscillation frequency control voltage (b) is fed to a varactor diode D2 of the local oscillation circuit 6. A desired frequency f1 is selected by the high amplifier stage 2, fed to a mixing circuit 4, added to the oscillation frequency f0 from the local oscillation circuit 6 to obtain an intermediate frequency of (f1-f0). In setting the value of elements for the tuning circuit within + or -5%, the reception sensitivity is maximized.
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