RCA BR200DV, Service Manual

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BR200DV/BR300DV
Service Manual
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
The audio signals after demodulation in IC200 may contain CTCSS (continuous tone control squelch
system) or DCS （ digital squelch ） signals. The spectrum component of CTCSS/DCS is 67 to 250Hz. The
filtering circuit composed of IC301 can filter out signals except CTCSS/DCS spectrum, which makes
MCU decode the CTCSS/DCS more accurately.
5.3 Transmitter (Tx)
Transmitter Power Amplifier
Figure 4 Schematic Diagram for Power Amplifier and Antenna Switch
The modulated RF signals from VCO are amplified by Q101 and Q105 before the power amplification
in Q107.