| 摘要 |
PURPOSE:To use an AM/FM amplifying circuit in the optimum state, by cutting highly the leakage component of the AM local oscillating frequency only in an AM reception mode by a switching operation of a transistor. CONSTITUTION:An AM/FM changeover switch 12 is applied to a terminal (b) of the AM side. Thus a transistor TR11 is turned on. An AM intermediate frequency input applied to a terminal 1 is amplified by an AM/FM intermediate frequency amplifying circuit 10 amd delivered through an AM wave detecting terminal 7 after a wave detection carried out through an AM wave detecting circuit 5. While the leakage component of an AM local oscillating frequency is cut highly via a capacitor 9 and the TR11. Then the switch 12 is applied to a terminal (c) of the FM side. In this case, the base of the TR11 is opened and the TR11 is turned off. Then the FM interemediate frequency component supplied to a terminal 2 is amplified and then delivered through an FM wave detecting terminal 8 after a wave detection through an FM wave detecting circuit 6. In this case, the FM intermediate frequency component is never cut highly. |
