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 (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.
UHF2 receiver design covers the frequency range of 435 – 480 MHz.
VHF receiver design covers the frequency range of 136 – 174 MHz.
Harmonic
ANT-SW
filter (LPF)
CR401,
CR301
PRESELECTOR POST SELECTOR
LNA
FILTER
Q301
F.T.V.
Recovered AUDIO

Figure 2-1. Receiver Block Diagram

1'ST
MIXER
FILTER
VCO
Inj FILTER
DESCRIMINATOR
Cer filter Cer filter
CF1(FW) CF2(HW)
N/S SW
MCF
(X-tal filter)
45.1MHz
450C24
IF AMP
IF, MIX
Q303
U201
X-TAL
44.645MHz