Chapter 2 Theory Of Operation; Introduction; Uhf2 Transmitter; Power Amplifier - Motorola GP Series Service Manual

1.0

Introduction

This Chapter provides a detailed theory of operation for the UHF 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 UHF Transmitter
( Refer to Figure 2-1 and the UHF Transmitter schematic diagram )
The UHF 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 (PA) consists of two principle devices:
1. LDMOS PA driver IC, U101.
2. LDMOS PA final stage, Q110.
The LDMOS driver IC provides 2-stage amplification using a supply voltage of 7.3V. The amplifier is
capable of supplying an output power of 0.3W (pins 6 and 7) with an input signal of 2mW at 3dBm
(pin16). The current drain is typically 160mA while operating in the frequency range of 450-527MHz.
P CI C
Vcontrol
Power
Amplifier
P A
Driver
Figure 2-1 UHF Transmitter Block Diagram.
THEORY OF OPERATION
Vcontrol
Antenna Switch/
P A Final
St a g e
Harmonic Filter
Chapter 2
Antenna
Matching
Network