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 (438-470MHz) Receiver
The UHF receiver covers the range of 438-470 MHz and provides switchable IF bandwidth for use
with 20/25 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 1-1 UHF Receiver Block Diagram
THEORY OF OPERATION
Interstage
Crystal
Filter
1st Mixer
Inj Filter
6G
Ceramic
Resonator
Demodulator
12.5kHzFilter
Chapter 1
IF
Amp
Filter
BW_SEL
6E
Cer Fltr
Switching
4E