Chapter 2
THEORY OF OPERATION
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).
Figure 2-1 UHF Transmitter Block Diagram.
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.
PCIC
PA
Antenna Switch/
Driver
Stage
Harmonic Filter
Vcontrol
Vcontrol
From
Antenna
Matching
Network
Power
Amplifier
VCO
P A Final
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