| 摘要 |
PURPOSE:To allow the titled circuit to trace a rapid level fluctuation at the start of burst signal reception by controlling a pin diode connected to a peak value detection circuit so as to be conducted at the start of burst signal reception. CONSTITUTION:Since no signal is given to a transmission line signal input terminal 11 before a burst signal comes thereto, an equalizing amplifier 1 is in the maximum gain state. When the burst signal comes in this state, an excess current flows momentarily to an output terminal 12, a potential difference between an output terminal 14 of a peak value detection circuit 2 and an output terminal 15 of a time constant circuit 5 is increased momentarily, a diode D2 and a transistor (Tr) of a control circuit 16 are conducted and a current flows to the pin diode D1. Thus, the circuit 3 controls the amplifier 1 to decrease its gain via a DC amplifier 4 at a small time constant. Since a signal string with less level variance continues to the succeeding burst signal, the level differ ence between the terminals 14 and 15 is less, the D1 is nonconductive, the circuit 5 is operated in a time constant comprising a resistor R1 and a capacitor C1 to attain AGC operation via an amplifier 4.
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