Motorola GP series Service Information

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

Motorola GP series Specifications

General

Operating Temperature	-30°C to +60°C
Frequency Range	136-174 MHz
Number of Channels	16
Channel Spacing	12.5 kHz / 25 kHz
Battery Life	8 hours (with standard battery)
Operating Voltage	7.5V DC
Ingress Protection	IP54
MIL-STD	810 C, D, E, F