Motorola CP Series, Service Manual, Page: 35 / 154

Chapter 5 435 – 480 MHz UHF2 Theory Of Operation
5.1 Introduction
This chapter provides a detailed theory of operation for the radio components. Schematic diagrams
for the circuits described in the following paragraphs are located in Chapter 7 of this manual.
5.2 UHF2 Receiver
The UHF2 receiver design covers the frequency range of 435 – 480 MHz and it is a double
conversion super heterodyne with 1st IF 45.1 MHz and 2nd IF 455 kHz. The receiver is divided into
two major blocks, Front End and Back End as shown in Figure 5-1.
Figure 5-1. UHF2 Receiver Block Diagram
Crysta l
F i l ter
Crysta l
44.64 5M Hz
1st Mi x er
RF
A mp
Prese l ector
F i l ter
Postse l ector
F i l ter
RX f rom
A ntenna S w itc h
I n j F i l ter
F irst LO
f rom Synt h esi z er
IF
A mp
IF
A mp
L P F
Ceramic
F i l ter
D escriminator
4 55 FW
4 55 HW
Qu a d rat u re
D etector
R SS I
N /S _ S W
R eco v ere d Aud io
4 55C2 4