RCA BR200DV, Service Manual

Page: 25 / 79

BR200DV/BR300DV
Service Manual
25
Gate bias of Q105 and Q107 is controlled by APC circuit, so the output power of transmitter can be
controlled conveniently by changing the gate bias voltage.
APC
（
Automatic Power Control
）
Figure 5 Schematic Diagram for APC Circuit
R130 R131 and R132 are power amplification current detector, IC100A is power amplification current
sampling amplifier and IC00B is power comparison amplifier.
The power amplification current and IC100A output will increase with oversized output power of
transmitter. When the output voltage of IC100B decreases, the bias voltage of Q105 and Q107 will
decrease, finally the output power of transmitter will decrease or vice versa. Thus, the output power of
transmitter will keep stable under any different working condition.
MCU can set the power by changing the voltage input to IC100B.
Audio Signal Processing of Transmitter
Figure 6 Schematic Diagram for Audit Circuit of Receiver
The audio signal processing circuit of Transmitter consists of IC601 and IC609. Voice signals from
MIC are sent to VCO for modulation together with CTCSS/DCS after amplification, limitation and filtering.
IC609 is a bais band processor.
AGC circuit consists of D601, D602 and Q602,Q603. The signal amplitude is reduced to ensure no