Chapter 2
THEORY OF OPERATION
1.0
Introduction
This Chapter provides a detailed theory of operation for the VHF circuits in the radio. Schematic
diagrams and board layout diagrams are included in Chapter 4 in this Section of the manual.
2.0
VHF (146-174MHz) Receiver
The VHF receiver covers the range of 146-174 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
Figure 2-1
VHF Receiver Block Diagram
Demodulator
Crystal
Filter
1st Mixer
RF
Amp
IF
Amp
Preselector
Filter
Interstage
Filter
Recovered Audio
RSSI
RX from
Antenna Switch
Inj Filter
First LO
from Synthesizer
Ceramic
Resonator
Cer Fltr
Switching
4E
6E
6G
BW_SEL
12.5kHzFilter
Содержание CP 140
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