Chapter 2 Theory Of Operation; Introduction; Vhf Transmitter; Power Amplifier - Motorola Professional GP340 Service Manual

1.0

Introduction

This Chapter provides a detailed theory of operation for the VHF circuits in the radio. For details of
the theory of operation and trouble shooting for the the associated Controller circuits refer to the
Controller Section of this manual.
2.0

VHF Transmitter

( Refer to Figure 2-1 and the VHF Transmitter schematic diagram )
The VHF transmitter consists of the following basic circuits:
1. Power amplifier (PA).
2. Antenna switch/harmonic filter.
3. Antenna matching network.
4. Power Control Integrated Circuit (PCIC).
From
VCO
2.1

Power Amplifier

The power amplifier consists of two devices:
1. LDMOS driver IC (U3501)
2. LDMOS PA (Q3501)
The LDMOS driver IC contains two stages of amplification with a supply voltage of 7.3V.
PCIC
Vcontrol
Power
Amplifier
PA
Driver
Figure 2-1 VHF Transmitter Block Diagram.
THEORY OF OPERATION
Vcontrol
PA Final Antenna Switch/
Stage
Harmonic Filter
Chapter 2
Antenna
Matching
Network