Chapter 4: Circuit Description; Receiver System; Transmitter System - Motorola EVX S24 Service Manual

MN006437A01-AB
Circuit Description
Chapter 4
Circuit Description
4.1

Receiver System

Front-End RF Amplifier
Incoming RF signal from the antenna passes through the low-pass filter, antenna switching diode
D1011/D1014 (both 1SS390), and band-pass filter. The filtered RF signal is applied to the amplifier
Q1033 (MAX2373ETC+T), then remove the undesired frequen- cies by another band-pass filter. The
amplified RF signal is applied to the custom IC Q1046 (RODINIA).
Demodulator
The custom IC Q1046 (RODINIA) converts a Base Band signal by mixing the RF signal with the local
signal, and then the Base Band signal is demodulated by the another section of the custom IC Q1046
(RODINIA). The local signal is generated by the VCO which consists of Q1036 (BFR460L3) and
varactor diodes D1029/D1030/D1031/D1032 (all 1SV279).
Audio Amplifier
The demodulated signal is adjusted the audio volume level in the custom IC Q1046 (RODINIA). The
adjusted the audio signal is applied to the audio amplifier U1700(TPA6211A1DRBR). As a result, the
audio signal provides up to 500 mW (@4 ohm BTL) for internal speaker and external speaker.
4.2

Transmitter System

MIC Amplifier and Modulator
The speech signal from internal microphone MC2001 on the DISPLAY Unit or external microphone
J1005 on the MAIN Unit is supplied to the custom IC Q1046 (RODINIA), which modulates the speech
signal to the FM or digital signal.
Drive and Final Amplifier Stages
The modulated signal from the custom IC Q1046 (RODINIA) is buffered by Q1034 (2SK3077) and
amplified by driver amplifier Q1026 (RD01MUS2B). The low level transmit signal is then applied to
Q1016 (RD04LUS2) for final amplification up to 3 watts output power. The transmit signal then passes
through the antenna switch D1009/D1053 (both RN142S) and is low-pass filtered to suppress away
harmonic spurious radiation before delivery to the antenna.
Automatic Transmit Power Control
The current detector Q1006-1 (AD8566ARM) detects the current of the final amplifier Q1016
(RD04LUS2) and the driver amplifier Q1026 (RD01MUS2B), and converts the current difference to the
voltage difference. The output f rom the current detector Q1006 - 1 (AD8566ARM) is compared with
the reference voltage and amplified by the power control amplifier Q1006-2 (AD8566ARM). The output
from the power control amplifier Q1006-2 (AD8566ARM) controls the gate bias of the driver amplifier
Q1026 (RD01MUS2B) and the final amplifier Q1016 (RD04LUS2). The reference voltage changes into
two values (Transmit Power High and Low) controlled by custom IC Q1046 (RODINIA).
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