Chapter 2 Theory Of Operation; Introduction; Major Assemblies; Receiver - Motorola CP185 Basic Service Manual

Chapter 2 Theory Of Operation

2.1

Introduction

This chapter provides a basic theory of operation for the radio components.
2.2

Major Assemblies

• Main PCB – Contains the RF circuits which comprises receiver, transmitter, phase-locked loop
(PLL) frequency synthesizer, micro controller, power supply, audio and digital circuits
• Display and Keypad PCB (Limited and Full Keypad models only) – 8 characters (14 segments
star burst) and 10 icons with backlighting, liquid-crystal display (LCD)
• Volume Knob PCB (PMDN4129AR) – Rotary Volume Knob
• Volume Knob PCB (PMDN4128AR) – Rotary Volume Knob and 16-channel Knob
2.2.1

Receiver

The radio's receiver is a double conversion super heterodyne with 1st IF of 45.1 MHz and 2nd IF of
455 kHz.
UHF1 receiver design covers the frequency range of 403 – 447 MHz.
UHF2 receiver design covers the frequency range of 435 – 480 MHz.
VHF receiver design covers the frequency range of 136 – 174 MHz.
RX from
Antenna Switch
Preselector RF Postselector
Filter Amp
First LO
from Synthesizer
N/S_SW
Descriminator
Recovered Audio
RSSI

Figure 2-1. Receiver Block Diagram

Crystal
Filter 1st Mixer
Filter
Inj Filter
Ceramic
455C24
LPF
Quadrature
Detector
IF
Amp
Filter
455FW
455HW
IF
Amp
Crystal
44.645MHz