| 摘要 |
PURPOSE:To obtain a gain most suitable for respective electric field areas by providing an automatically operating point changing means for changing the operating point automatically according to an electric field strength. CONSTITUTION: When an electric field strength of an electric wave 100, for instance, is increased, a gain control voltage 300 fed back from an automatic gain control section 41 of a detecting circuit 4 becomes small and is controlled so as to make small a gain of a tuner 2. Therefore, partial potentials of resistances 15, 16 impressed to a base of a transistor TR 14 are lowered in accordance with a part in which the control voltage 300 is made small and the TR is turned on. Then, a power source voltage Vcc short circuits a resistance 13 and then is directly impressed to a volume 5. Therefore, a delay point setting voltage impressed to the control section 41 from the volume 5 is raised, so as to make fast the delay point, an operating point of an automatic gain suitable for a strong electric field area and the gain of the tuner 2 is restricted.
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