Theory Of Operation; Introduction; Uhf3 (465-495Mhz) Receiver - Motorola CP140 Series Service Information

1.0

Introduction

This Chapter provides a detailed theory of operation for the UHF circuits in the radio. Schematic
diagrams and board layout diagrams are included in Chapter 4 in this Section of the manual.
2.0 UHF (465-495MHz) Receiver
The UHF receiver covers the range of 465-495 MHz and provides switchable IF bandwidth for use
with 20/25/30 kHz or 12.5 kHz channel spacing systems. The receiver is divided into two major
blocks, as shown in Figure 2-1.
Front End
Back End
RX from
Antenna Switch
Preselector RF
Filter Amp
First LO
from Synthesizer
Recovered Audio
RSSI
Figure 2-1 UHF Receiver Block Diagram

THEORY OF OPERATION

Interstage
Crystal
Filter 1st Mixer
Inj Filter
6G
Ceramic
Resonator
Demodulator
12.5kHzFilter
Chapter 2
IF
Amp
Filter
BW_SEL
6E
Cer Fltr
Switching 4E