Motorola CP Series, Service Manual, Page: 111 / 154

Chapter 11 403 – 447 MHz UHF1 Theory Of Operation
11.1 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 14 of this manual.
11.2 UHF1 Receiver
The UHF1 receiver design covers the frequency range of 403 – 447MHz and it is a double
conversion super heterodyne with 1st IF 45.1MHz and 2nd IF 455kHz. The receiver is divided into
two major blocks, Front End and Back End as shown in Figure 11-1.
Figure 11-1. UHF1 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