RCA BR200D-U1 Service Manual page 24

Receiving Audio Signal Processing:
The audio processing circuit of receiver consists of IC300. Voice signals from IC300 are sent to IC301
（CTCSS signaling filter circuit.
Squelch Circuit
Part of the AF signal from the IC200 enters the FM IC again,and the noise component is amplified
and rectified by a filter and an amplifier to produce a DC voltage corresponding to the noise level.
The DC signal from the FM IC goes to the analog port of the microprocessor(IC403).IC403
determines whether to output sounds from the speaker by checking whether the input voltage is higher
or lower than the preset value.
To output sounds from the speaker,IC403 sends a high signal to the MUTE and AFCO lines and turns
IC302 on through Q302 Q304 and Q305.
Audio Power Amplification
The audio power amplifying circuit consists of IC302 and the peripheral components.
The signals are amplified by audio power amplifier to drive the speaker after collecting the receiving
audio signals, voice signals and warning tone signals. The warning tone has no volume limitation.
When AFCO is high level, Q304 is on, IC302 begins to work and the speaker sounds. Speaker
Impedance: 16ohm
CTCSS Signal filtering
BR200D-U1/BR300D-U1 Service Manual
Figure 3 Schematic Diagram for IF System
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