Chapter 2
THEORY OF OPERATION
1.0
Introduction
This Chapter provides a detailed theory of operation for the UHF circuits in the radio. For details of
the theory of operation and trouble shooting for the the associated Controller circuits refer to the
Controller Section of this manual.
2.0
UHF (403-470MHz) Receiver
2.1
Receiver Front-End
The receiver is able to cover the UHF range from 403 to 470 MHz. It consists of four major blocks:
front-end bandpass filters and pre-amplifier, first mixer, high-IF, low-IF and receiver back-end. Two
varactor-tuned bandpass filters perform antenna signal pre-selection. A cross over quad diode
mixer converts the signal to the first IF of 44.85 MHz. Low-side first injection is used.
Figure 2-1
UHF Receiver Block Diagram
Demodulator
1. Crystal
Filter
Mixer
Varactor
Tuned Filter
RF Amp
Varactor
Tuned Filter
Pin Diode
Antenna
Switch
RF Jack
Antenna
Control Voltage
from PCIC
First LO
from FGU
Recovered Audio
RSSI
Second LO
2. Crystal
Filter
455kHz Filter
(25kHz)
455kHz Filter
(25kHz)
455kHz Filter
(12.5kHz)
455kHz Filter
(12.5kHz)
Switch
Switch
Switch
Switch
Limiter
1. IF Amp
2. IF Amp
Filter Bank Selection
from Synthesizer IC
Harmonic
Filter
BWSELECT
Summary of Contents for 6864115B62-C
Page 1: ...Professional Radio GM Series Detailed Service Manual 6864115B62 C ...
Page 2: ...ii ...
Page 4: ...iv ...
Page 5: ...Professional Radio GM Series Service Maintainability Issue July 2007 ...
Page 8: ...ii ...
Page 22: ...2 10 MAINTENANCE ...
Page 25: ...Professional Radio GM Series Controlhead Service Information Issue July 2007 ...
Page 77: ...Professional Radio GM Series Controller Service Information Issue May 2007 ...
Page 100: ...2 2 TROUBLESHOOTING CHARTS ...
Page 104: ...3 4 Controller schematics parts list ...
Page 154: ...3 52 Controller T12 Schematic Diagrams ...
Page 155: ...Professional Radio GM Series VHF 136 174MHz Service Information Issue May 2007 ...
Page 164: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 176: ...2 12 THEORY OF OPERATION ...
Page 186: ...3 10 TROUBLESHOOTING CHARTS ...
Page 190: ...4 4 VHF PCB SCHEMATICS PARTS LISTS ...
Page 252: ...4 66 VHF 1 25W PCB 8471235L02 Schematics VHF 136 174 MHz IF ...
Page 256: ...4 70 VHF 1 25W PCB 8471235L02 Schematics ...
Page 257: ...Professional Radio GM Series UHF 403 470MHz Service Information Issue May 2007 ...
Page 266: ...1 6 MODEL CHART AND TECHNICAL SPECIFICATIONS ...
Page 366: ...2 12 THEORY OF OPERATION ...
Page 372: ...3 6 Low Band TROUBLESHOOTING CHARTS ...