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Section 7: 2-1
Chapter 2
THEORY OF OPERATION
1.0
Introduction
This chapter provides a detailed theory of operation for the low band circuits in the radio. For details
of the theory of operation and troubleshooting for the associated controller circuits refer to the
controller section of this manual.
2.0
Low Band Receiver Front-End
2.1
Receiver Front-End
The low band receiver, shown in Figure 7-1, is bandsplit into three ranges depending on radio
model, covering frequencies from 29.7 to 36.0 MHz, 36.0 to 42.0 MHz, or 42.0 to 50.0 MHz. The
circuitry of the three models is identical except for component value differences. The receiver
consists of five major blocks: front-end bandpass filters and pre-amplifier, first mixer, high-IF and
blanker switches, low-IF and receiver back-end, and
“Extender”
(noise blanker). Two fixed-tuned
bandpass filters perform antenna signal pre-selection. A passive double-balanced mixer converts
the signal to the high-IF of 10.7 MHz. High-side first injection is used.
Figure 7-1
Low Band Receiver Block Diagram
1
Demodulator
Delay
Filter
Mixer
Fixed
Tuned Filter
RF Amp
Tuned Filter
Pin Diode
Antenna
Switch
RF Jack
Antenna
First LO
RXINJ
Recovered Audio
RSSI
IF
Second LO
Crystal
Filter
455kHz Filter
455kHz Filter
455kHz Filter
(12.5kHz)
455kHz Filter
(12.5kHz)
Swit
ch
Swit
ch
Swit
ch
Swit
ch
Limiter
IF Amp
IF Amp
Filter Bank Selection
from Synthesizer IC
Blanker
Noise
Blanking Pulses
Gate
Buffer
Enable
1st
Fixed
(25/20kHz)
BWSELECT
(U1201 Pin 48)
4-pole
(25/20kHz)
Summary of Contents for PRO Series
Page 1: ...CDM Series and PRO Series Two Way Mobile Radios Detailed Service Manual 6881091C63 F ...
Page 4: ...Notes ...
Page 6: ...Notes ...
Page 8: ...Section 1 ii 6881091C63 F Notes ...
Page 12: ...Section 1 1 4 Radio Model Information 6881091C63 F Notes ...
Page 22: ...Section 1 2 10 Notes For All Schematics and Circuit Boards 6881091C63 F Notes ...
Page 46: ...Section 2 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 78: ...Section 3 1 20 Controller Board Audio and Signaling Circuits Section 6881091C63 F Notes ...
Page 80: ...Section 3 2 2 Troubleshooting Flow Chart for Controller 6881091C63 F Notes ...
Page 84: ...Section 3 3 4 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 146: ...Section 3 3 66 Controller T6 T7 Schematics and Parts Lists 8471235L06 Notes 6881091C63 F ...
Page 152: ...Section 4 1 4 Technical Specifications 6881091C63 F Notes ...
Page 168: ...Section 4 3 8 Troubleshooting Flow Chart for VCO 6881091C63 F Notes ...
Page 172: ...Section 4 4 4 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 232: ...Section 5 1 4 Technical Specifications 6881091C63 F Notes ...
Page 242: ...Section 5 2 10 UHF Band 1 403 470 MHz 1 25 W Frequency Synthesis 6881091C63 F Notes ...
Page 296: ...Section 6 1 4 Technical Specifications 6881091C63 F Notes ...
Page 306: ...Section 6 2 10 UHF Band 2 450 512 527 MHz 1 25 W Frequency Synthesis 6881091C63 F Notes ...
Page 316: ...Section 6 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 352: ...Section 7 3 6 Troubleshooting Flow Chart for VCO 6881091C63 F Notes ...
Page 356: ...Section 7 4 4 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 458: ...Section 8 1 4 Technical Specifications Section 6881091C63 F Notes ...
Page 474: ...Section 8 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 496: ...Section 9 1 4 Technical Specifications Section 6881091C63 F Notes ...
Page 512: ...Section 9 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 530: ...Section 10 1 4 Technical Specifications Section 6881091C63 F Notes ...
Page 546: ...Section 10 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 564: ...Section 11 1 4 Technical Specifications 6881091C63 F Notes ...
Page 580: ...Section 11 3 8 Troubleshooting Flow Chart for VCO 6881091C63 F Notes ...
Page 582: ...Section 11 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 608: ...Section 12 1 4 Technical Specifications 6881091C63 F Notes ...
Page 624: ...Section 12 3 8 Troubleshooting Flow Chart for PassPort 6881091C63 F Notes ...
Page 626: ...Section 12 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...
Page 654: ...Section 13 1 4 Technical Specifications 6881091C63 F Notes ...
Page 672: ...Section 13 4 2 Allocation of Schematics and Circuit Boards 6881091C63 F Notes ...