| 摘要 |
PURPOSE:To attain ease of gain control and stabilization against a large input by using the adjustment of large input gain in common at a large input so as to obtain a control voltage changed corresponding to the true large input. CONSTITUTION:An AGC current is increased in the AGC operation in responce to the large input and flows to the emitter of a transistor TR56 from a voltage/current converting circuit 68. A voltage drop is generated across a resistor 58 by the AGC current and the emitter potential is increased. The potential between the base and emitter of the TR56 is decreased, a currnent flowing to the TR56 is a minute current and its current value is decreased exponentially in response to the large input. Thus, the AGC current is increased. When the AGC voltage of the TR56 is increased, the base voltage of the TR54 is increased and when the TR54 is conducted, a TR52 is conductive and the input signal of a frequency mixer circuit 4 is suppressed by the short-circuit of a primary coil of the tuning coil 16.
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