Control manner of automatic gain control circuit of the amplifier for CATV and the amplifier null for CATV

摘要

PURPOSE:To optionally change the reference gain of an amplifier AGC circuit by switching a changeover switch to the side of a reference gain control part with an instruction from the side of a center unit to a status monitor. CONSTITUTION:When prescribed gain can not be obtained due to the fault of the down stream amplifier of an amplifier 1, signal strength is decreased for the gain of the fault amplifier at a terminal and irregularities in images is generated. At this time, at the side of the center unit, a required reference gain value is calculated and instructed to a CPU 71. The reference gain control part 73 sets the reference gain with the instruction. Then, the control part 73 is connected to a DC amplifier 14, an AGC circuit 10 is operated with the set reference gain and the gain is controlled. In such a manner, thereafter, the reference gain of the circuit 10 is the value set at the control part 73 with the center unit side instruction and the gain is automatically controlled with the value as a reference. Thus, the decrease of the signal strength due to the fault of the lower stage amplifier can be compensated. After the recovery of the fault, the circuit 10 returns to an automatic gain control state based on the conventional prescribed reference gain.