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Maintenance Manual
MONOGRAM SERIES
PORTABLE RADIO
SWITCHABLE VHF/UHF
e
Copyright
August 1996, Ericsson, Inc.
This manual covers Ericsson and General Electric products manufactured and sold by Ericsson Inc.
NOTICE!
Repairs to this equipment should be made only byan authorized service technician or facility designated by the supplier. Any
repairs,alterations or substitution of recommended parts made by the user to this equipment not approved by the manufacturer
could void the user’s authority to operate the equipment in addition to the manufacturer’s warranty.
NOTICE!
This manual is published by Ericsson Inc., without any warranty. Improvements and changes to this manual necessitated by
typographical errors, inaccuracies of current information, or improvements to programs and/or equipment, may be made by
Ericsson Inc., at any time and without notice. Such changes will be incorporated into new editions of this manual. No part
of this manual may be reproduced or transmitted in any form or by any means, electronic or mechanical, including
photocopying and recording, for any purpose, without the express written permission of Ericsson Inc.
The software contained in this device is copyrighted. Unpublished rights arereserved under the copyright laws of the United
States.
NOTICE!
SWITCHABLE VHF AND UHF RADIO
Page-i-
TABLE OF CONTENTS
SPECIFICATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
UNPACKING INFORMATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
GENERAL FEATURES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
MAIN FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Scan Mode. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Scan Channel Delete. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Scan Delay Time. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Busy Channel Lockout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Marked Idle Enable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Normal / Inverted DCS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Standard / Non-Standard Channel Guard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Transmit Time Out Timer / TX Inhibit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Beep Tone Enable / Disable . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Receive Condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Low Battety Indication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
External Option Detect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Monitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Diagnostic Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
DISCRIPTION OF CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
CIRCUIT ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
DIGITAL BOARD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
CG/DCG Decode Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
CG/DCG Encoder Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
External MIC/PTT Control Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Channel Select Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Battery Low Indicator Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
EEPROM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
High Pass Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Mute (Squelch) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
TX Audio and Filter Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Analog Ground Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Audio Mixer and Invertor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
RF BOARD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VHF Transmitter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Microphone Audio Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Transmitter Stage and Harmonic Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Automatic Power Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Frequency Synthesizer Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
VHF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Voltage Controlled Oscillator Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
SWITCHABLE VHF AND UHF RADIO
TABLE OF CONTENTS
Page-ii-
First Mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Second Oscillator Mixer Limiter and FM Detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Squelch (Mute) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
16 kHz Band Pass Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Noise Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Low Pass Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Speaker Audio Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
UHF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Microphone Audio Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Transmitter Stage and Harmonic Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Automatic Power Control. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Frequency Synthesizer Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
Voltage Controlled Oscillator Module. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Receiver. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
First Mixer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Second Oscillator Mixer Limiter and FM Detector. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Squelch (Mute) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
16 kHz Band Pass Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Noise Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Low Pass Filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Speaker Audio Amplifier. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
PLL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
MAINTENANCE AND REPAIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
GENERAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
UHF . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
VHF. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
REMOVING AND REPLACING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Removing And Replacing The Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Removing And Replacing The Microphone And Speaker . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Removing and Replacing the Control PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
Removing and Replacing the PCB Shield Plate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
Removing and Replacing the RF PCB . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
ALIGNMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
RECEIVER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
TRANSMITTER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
TCXO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
VHF VCO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
UHF VCO. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Channel Guard Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Transmitter Modulation Deviation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
High/Low Power Adjust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
PERFORMANCE TEST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Test Equipment Required . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Test Equipment Connection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Power Supply Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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Audio and PTT Connections. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
Prerequisites. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
EEPROM Programming for Alignment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
TRANSMITTER PERFORMANCE TESTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Power Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
Peak Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Spectrum Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
RECEIVER PERFORMANCE TEST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
SINAD Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
Noise Quieting Sensitivity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Squelch Sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
Audio Output. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
COMPONENT REPLACMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
SURFACE MOUNT COMPONENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
SURFACE MOUNT REMOVAL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
SURFACE MOUNT COMPONENT REPLACEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
SURFACE MOUNTED INTEGRATED CIRCUIT REPLACEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
TROUBLESHOOTING CHARTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
VOLTAGE CHARTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36
LINK OPTION DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
TRANSISTOR AND IC PINOUT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
ELECTRICAL PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
VHF PARTS LIST. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
UHF PARTS LIST . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
ASSEMBLIES COMMON TO VHF AND UHF RADIOS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58
SCHEMATICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
OUTLINE DIAGRAMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
SWITCHABLE VHF AND UHF RADIO
TABLE OF CONTENTS
Page-iv-
SPECIFICATIONS
The information detailed in the Specifications is for the VHF and UHF Series hand portable radios. Unless otherwise stated the
information is the same for both.
General
Power Supply Rechargeable Nickel-Cadmium Battery, 10.8 VDC
Power Supply Voltage Range 9.2 V DC-13.5 V DC
Current Consumption
Standby < 20 mA (Battery Save On)
< 40 mA (Battery Save Off)
Receive < 250 mA (Max Audio)
Transmit < 1800 mA (5W)
Battery Life (5-5-90% duty cycle)
Typically
Standard Capacity Battery 7 hrs.. at 5W (save on), 5 hrs.. at 5W (save off).
High Capacity Battery 12 hrs.. at 5W (save on), 9 hrs.. at 5W (save off).
Environmental Designed to meet EIA / TIA 603
Temperature Range
-30° C to + 60 ° C
Relative Humidity
90% at 40 ° C Non-condensing
Speaker Impedance 8 ohm
Frequency Control PLL Synthesizer
Number of RX/TX Channels 16 Maximum
Frequency Bands
Operational Bandwidth
RX TX
VHF Band 148 MHz to 174 MHz 148 MHz to 174 MHz
UHF Band 400 MHz to 440 MHz 400 MHz to 440 MHz
UHF Band 440 MHz to 470 MHz 440 MHz to 470 MHz
SWITCHABLE VHF AND UHF RADIO
SPECIFICATIONS
Page-1-
Dimensions (mm)
Radio 99(H) x 64(W) x 36(D)
Standard Capacity Battery 59(H) x 64(W) x 36(D)
High Capacity Battery 84(H) x 64(W) x 36(D)
Weight
Radio 270 gm
Standard Capacity Battery 230 gm
High Capacity Battery 300 gm
Controls
Volume On/Off Switch Used to turn radio On/Off and set the Volume
Channel Select Switch Used to select one of four or one of sixteen channels,
depending on radio.
Press To Talk Button Used to Transmit (Referred to as PTT)
Monitor Button Push to Monitor
Hi/Low Power Button Push to change from 1 to 5 watts.
Accessories Socket 6 way socket, used for connecting the remote
speaker/microphone and programming.
Transmitter
Output Power Variable 1W or 5W nominal
RF Load Stability Unconditionally stable into a 10:1 VSWR at any phase angle.
RF Power Stability +2 dB - 3 dB of nominal power
(-30 ° C to +60 ° C).
Conducted Spurious Emissions -60 dBc max.
Radiated Spurious Emissions -60 dBc max.
Adjacent Channel Noise Power < 70 dBc @ 25 kHz.
< 70 dBc @ 20 kHz.
< 60 dBc @ 12.5 kHz.
Modulation System FM (F3E)
Audio Frequency Response +1/-3dB 500-3000 Hz @ 25 kHz Channel Spacing
Audio Harmonic Distortion < 5% at 60% System Deviation modulated with 1 kHz.
SWITCHABLE VHF AND UHF RADIO
SPECIFICATIONS
Page-2-
Maximum Deviation
± 5 kHz at 25 kHz BW
± 4 kHz at 20 kHz BW
± 2.5 kHz at 12.5 kHz BW
Microphone Sensitivity Better than 94 dB S.P.L.
Hum and Noise (Unsquelched)
≥ 40 dB @ 25 kHz Channel Spacing
Receiver
Sensitivity (12dB Sinad) UHF < -118dBm (0.28uv)
VHF < -119dBm (0.25uv)
Adjacent Channel Signal Selectivity > 70 dB @ 25 kHz.
> 70 dB @ 20 kHz.
> 60 dB @ 12.5 kHz.
Spurious Response Rejection
≥ 70 dBc
Avg. System Frequency Deviation 60% of peak at 1 kHz
Blocking
≥ 85 dB
Intermodulation Rejection >70 dB
Max Audio Power Output
0.5 W min. at 5% THD into 8 Ω
AF Distortion
2.0% THD at 200 mV into 8 Ω
Frequency Response 6 dB/octave de-emphasized response in the range 300
Hz-3000 Hz.
Hum and Noise (Unsquelched) > 40 dB
Conducted and Radiated Spurious Emission Per FCC and DOC Rules and Regulations
Temperature Stability
0.0005% (-30 ° C To +60 ° C)
Amplitude Characteristic <1dB
• Due to continuing research and development the company reserves the right to alter these specifications
without prior notice.
SWITCHABLE VHF AND UHF RADIO
SPECIFICATIONS
Page-3-
UNPACKING INFORMATION
Check the carton and packing material carefully for the following items:
1. Transceiver Unit
2. Belt Clip
3. Operator’s Manual
4. Antenna
∗
Options:
5. Battery
Packing is cardboard tray box.
SWITCHABLE VHF AND UHF RADIO
UNPACKING INFORMATION
Page-4-
INTRODUCTION
Advanced state-of-the-art technology is used in the design and manufacturing of the VHF and UHF scanning hand-helds. The
Phase Lock Loop (PLL) synthesizer provides more flexibility and capability in a radio than ever before offered. The VHF and
UHFscanninghand-heldshas upto16 channel capability,dependingon which modelischosen. ItoffersCTCSS,DCS,scanning,
priority channel, and many other functions. All these functions are controlled by the micro controller. The micro controller reads
specific channel information from an Electronically Erasable Read Only Memory (EEPROM).
SWITCHABLE VHF AND UHF RADIO
INTRODUCTION
Page-5-
GENERAL FEATURES
MAIN FEATURES
•
Switchable
• Scan Mode
• Busy Channel Lockout / Marked Idle Enable
• Channel Guard (CG) / Digital Channel Guard (DCG)
• Transmit Time Out Timer / TX Inhibit
• Beep Tone Enable/disable
• Low Battety Indication
• Memory Protect
• External Option Detect
• 16 Channel
Scan Mode
During programming of the radio any channel can be selected as a scanned channel. When a channel is selected as a scanned
channel it becomes part of the scan list. The scan list will be activated by switching to the channel that was selected as the scan
list channel during programming of the system parameters. The channel that was selected as the scan list channel can still be used
as a receive only channel when in scan mode or receive and transmit channel if the channel has been programmed for “wait time
transmit”.
Scan Channel Delete
When the unit is in scan mode the monitor button can be pushed to delete a channel from the scan list. If the monitor button is
pushed while scanning has stopped to monitor an activechannel, that channel will be deleted from the scan list. The channel will
remain inactive in the scan list until the scan mode is re-initiated by switching off the scan list channel and switching back to the
scan list channel. Any number of channels can be deleted from the scan list in this way. The scan list is always initiated with all
scan list channels active.
A primary operating channel can be selected while programming the radio. A primary operating channel is a channel that can be
periodically checked or looked back at while receiving on any channel selected during programming. It can also be selected for
all transmissions during scan mode.
To transmit on a channel in the scan list, the channel selector must be placed on the channel that the transmission is to be made
on. As a system programmable option, it is possible to transmit on a scanned channel while the channel selector is on the scan
list channel. This is the “wait time transmit” option. If this option is enabled, the PTT can be pushed during the scan wait time
and the transmission will be on the channel that was just activated. If this option is disabled, the transmission will be on the look
back channel or the selected channel.
Any channel whether it is in the scan list or not, can be designated as a look back channel. When a channel is designated as a
look back channel and the channel is selected, the radio will periodically look back at the priority channel during reception on
the selected channel. The radio does not have to have a scan list entered to have this function. The radio must have a look back
channel selected for the function to work.
SWITCHABLE VHF AND UHF RADIO
GENERAL FEATURES
Page-6-
• NOTE: The programmer dis-allows the programming of a channel as look back channel activated if no
priority channel was selected.
The channel scan speed is system programmable in a range of 20 milliseconds to 2 seconds in 10 millisecond increments. The
default value is 100 milliseconds.
Scan Delay Time
Scan delay time is system programmable. The scan delay time is the time that the unit remains on a scanned channel, after
receiving or transmitting on that channel. The time is programmable from 1 to 10 in 1 second increments. The default value is 4
seconds.
The Scan delay time will be reset each time the receive channel is active and each time the PTT is pushed on that channel. As
long as the conversation continues on the channel, the receiver or the transmitter is active before the scan delay time expires the
unit will not resume scanning.
As a programmable option the LED on the top panel of the unit will flash at the scan rate while in the scan mode. If the “LED
scan indication” is programmed to enable, the LED will flash. If it is programmed to disable, the LED will not flash.
Busy Channel Lockout
If enabled,theunitwillnot transmitduring areceivedsignal,carrier, carrier and incorrecttoneor DCG code or carrier andcorrect
tone, or DCG code and a beep tone will sound when the PTT is depressed.
Marked Idle Enable
If this function is enabled, the unit will transmit provided that the correct programmed CG tone or DCG code has been decoded.
This function is essential for repeater operation.
Normal / Inverted DCS
Thisfunctionisselectedbychannelduringprogrammingoftheradio.Duringprogrammingofeachchanneloftheradioaselective
signaling option for TX and RX is selected. When the DCG signaling option is selected it can be selected as either Normal or
inverted. The selection can be made differently for TX and RX.
If DCG is selected as inverted for TX, the transmitter will encode an inverted DCG code. If the receiver is selected as inverted,
the receiver will decode inverted DCG.
Standard / Non-Standard Channel Guard
When programming a channel with Channel Guard any frequency from 55 to 260Hz can be selected in 0.1Hz increments. The
radio will be capable of encoding and decoding two non-standard CG tones.
Transmit Time Out Timer / TX Inhibit
The Time Out Timer is system programmable for 10 seconds to 990 seconds, in 10 second increments and can also be selected
as disabled. The default value is 10 seconds. The addition to this feature is a programmable lock out time that inhibits the radio
transmitter for a specified time after the time out time expires.
When the time out timer function is enabled and the TX inhibit function is disabled, the radio will transmit after the time out
timer time has expired and the PTT button is released and again depressed. With the TOT and TX enabled, the radio will not
transmit after the time out time has expired, even if the PTT is released and again depressed. Transmission will not be allowed
until the TX inhibit time has expired. TX inhibit time is system programmable from 5 to 60 seconds in 5 second increments. The
default value for the TX inhibit time is 5 seconds.
The radio will beep 1 time, 5 seconds before the TOT time expires. This will indicate to the user that the transmitter is about to
be locked out. If the PTT is released and depressed again anytime before the TOT time has expired, the TOT time will be reset.
SWITCHABLE VHF AND UHF RADIO
GENERAL FEATURES
Page-7-
If the beep tone enable/disable is set to disable the 1 beep will not be issued. The radio will beep 4 times when the TOT time
expires. After the TX inhibit time passes, the radio will beep one final time.
Beep Tone Enable / Disable
This function will be programmable as a system function while programming the radio. When this function is set to enable, all
tones and warning beeps will be heard through the speaker of the radio. When this function is disabled, no beeps or tones will
be heard through the speaker. All indications will be visual only.
Receive Condition
This function is system programmable. If it is selected as enabled the unit will scan for carrier only. This will enable faster scan
rates. If this function is set to enable, CG and DCG cannot be selected on any channel. If this function is selected as disabled, all
options can be used on any channel.
Low Battety Indication
Low BATTERY Indication will not inhibit RX and will allow 1 transmission after low cell is indicated. Low Cell will not be
indicated during transmit mode. If the battery goes below specified limits during the TX mode, low cell will be indicated
immediately after releasing the PTT button. After the low cell indication is issued, the transmitter can only be used one time.
When the PTT is pushed again and then released, the transmitter is locked out until the unit is powered down and then powered
back up.
External Option Detect
An input to the microprocessor is available that will indicate to the microprocessor that the external option has decoded. This
input should be connected to the external option connector. External option should be selectable for each channel. If a channel
is selected during programming for external option, this input should be active when the channel is selected during operation of
the unit.
Monitor
The unit contains a switch mounted on the PTT assembly for monitor function. This can be enabled or disabled by programming
software.
Diagnostic Function
The Diagnostic function is designed to inform the user about the radio operating status. The possible audible warnings and
indications are:
Should any of the error messages listed below appear, the user should consult the dealer from whom the unit was purchased so
that the radio can be serviced by a qualified service technician.
TABLE 1-Status Indications And Audible Tones
STATUS DESCRIPTION LED COLOR AUDIBLE TONE
NORMAL Power on ready N/A Melody
Busy Yellow N/A
Correct Tone Green N/A
Transmit Red N/A
Scan Green, Flashing N/A
Busy Lock Yellow, Flashing Single Tone
WARNING Time Out Timer N/A Single Tone
Battery Low Red, Flashing Four Tone, Repeated
ERROR EEPROM Error Red, Flashing Single Tone, Repeated
PLL Error Red, Flashing Double Tone, Repeated
Filtering Error Red, Flashing Three Tone, Repeated
SWITCHABLE VHF AND UHF RADIO
GENERAL FEATURES
Page-8-
DISCRIPTION OF CONTROLS
The controls, indicators, accessories socket and antenna connections on the VHF and UHF Scanning Handheld Series radios are
all located on the top panel. The monitor and PTT buttons are located on theradio chassis left hand side. Figure 1 details theVHF
and UHF Scanning Handheld controls, indicators and connections.
Figure 1 - Controls and Indicators
SWITCHABLE VHF AND UHF RADIO
DISCRIPTION OF CONTROLS
Page-9-
TABLE 2-Controls, Indicators And Connections
ITEM: FUNCTION:
1. Antenna Connector 1/4 in UNEF socket.
2. Accessories Connector Multipurpose socket used to connect to a remote speaker/microphone,
programming cable or VOX unit.
3. ON/OFF Volume Control Main power switch and volume control. Fully counter clockwise is off
position.
4. Channel Select Switch Rotary switch, used to select one of 4 or one of 16 channels
(maximum) and to engage scanning function.
5. Status Indicator (busy
TX/BT)
Tri-colored LED indicator.
6. Hi/Low Power Button Push to change power level (5 watts or 1 watt).
7. Monitor Button When pressed, monitors the chosen channel. (unless prog. disabled)
8. Push-To-Talk Button Push to talk, release to listen.
9. Battery Pack Push to change power level (5 watts or 1 watt).
10. Speaker Sound reception.
11. Microphone Sound transmission
12. Battery Charge Contacts Charging contacts
SWITCHABLE VHF AND UHF RADIO
DISCRIPTION OF CONTROLS
Page-10-
CIRCUIT ANALYSIS
The VHF and UHF Scanning Handheld series radios are comprised of two main PCB’s ( an RF PCB and a Digital PCB). The
RF PCB contains the Transmitter and Receiver circuits. The Digital PCB contains the Micro controller and associated digital
circuits.
DIGITAL BOARD
U 411 Is a digitally-controlled analog switch which internally consist of three single pole, double throw switches. Placing a high
( 5V ) or low ( 0V ) on the control lines connect to the X1 or X0. Example: A high on control line A would connect X to X1 .
A low on control line would connect X to X0 .
CG/DCG Decode Circuits
Discriminator audio from Pin 15 CON 402 is fed into R470 and associated parts, which are the first 2 poles of a 6th order 250Hz
Chebeyshev low pass filter. The output from Pin 1 (U406A ) is fed into U411B (Pin 2) and output to Pin 15 (U411B). The signal
is then fed to Pin 8 (U407) which is a 6th order low pass Butterworth switched capacitor filter. The output from the Butterworth
filter (Pin 3 U407) is then fed to the remaining 4 poles of the 6th order Chebeyshev, which consist of U406C and one of the two
operational amplifiers internal to U407 (MF6-100) along with associatedcomponents.Both the Chebeyshev and the Butterworth
combine for a 4dB ripple low pass filter when programmed for 250Hz . The output of U406C (Pin 8) is fed into the remaining
operational amplifier internal to U407 (MF6-100) which forms the squaring circuit for the decode signal. The signal is output
from Pin 2 U407 (MF6-100) and fed into U409 (micro) where it is matched with a preprogrammed frequency. If a successful a
decode occurs, which is shown by a green LED on the top panel of the VHF and UHF Scanning Handheld, and audio is heard.
If a valid decode was not seen, the LED (Yellow) would be shown.
CG/DCG Encoder Circuit
During TX encode, the tone squelch digital signal is produced as a 3-bit parallel word at Pins 15 (A), 16 (B), and 18(C) of the
micro controller ( U409 ). The 3-bit digital signal is converted to an analog signal by resistors R478 , 479, and 480. The analog
signal is fed into U411B Pin 1. The signal is output on Pin 15 (U411B ) and fed into Pin 8 of U407 ( 6th order Butterworth clock
tuned low pass filter). The filtered encode output from Pin 3 (U407) is fed into Pin 13 ( U411A ) and output on Pin 14 (U411A
). The filtered encode signal is fed to U406B and RV403 (sub-audible gain control). The output of U406B is then fed to the
audio mixer circuit.
External MIC/PTT Control Circuit
When the external microphone is connected to the six pin Hiroshi connector on the top panel of the VHF and UHF Scanning
handheld , Pin 4 of the connector is shorted to ground, disabling the internal mic and internal speaker via pin 12 of Con 402 and
U402A . When external PTT is depressed, Pin 5 of the connector shorts to ground, which drops the voltage on Pin 1 (mic audio)
of the Con 500, to less than 2V . Pin 1 of the Con 500 is connected to U405D (Voltage Comparator) via R416 , R415, and Pin
11 of CON4 . When pin 13 of U405D goes below 2V, theoutput of U405D (Pin 14) goes high ( 5V )and turns on Q402., Q402’s
output is in parallel with the internal PTT line, which is connected to U409 (micro), Pin 24.
Channel Select Circuit
One of 16 channels may be selected using the channel switch on the top panel. The channel switch encodes the channel number
selected into a 4-Bit binary code. The binary code plus 1 is equal to the channel number. The binary code is decoded by the micro
controller enabling the appropriate RX or TX frequency and associated data to be selected from the EEPROM>
• NOTE: It is possible any one of the 16 channel locations can be a scanning position. Refer to Operator’s
Manual for further instructions.
SWITCHABLE VHF AND UHF RADIO
CIRCUIT ANALYSIS
Page-11-
Battery Low Indicator Circuit
When the battery voltage drops below 8.8VDC , U405A (Voltage Comparator) turns on Q403 . The micro controller disables
the transmitter and at the same time enablesthe red LED and sends an alert tone to warn the user. The battery should be replaced
or recharged at this time (one TX allowed after low battery).
EEPROM
RX/TX channels, CG/DCG as well as other data from the programmer are stored in the EEPROM. The data stored is retained
without power supplied. This is a non-volatile memory. The EEPROM may have information re-programmed or erased. U408
is an EEPROM with 2048 ( 8x256 ) capacity and data is written and read serially.
High Pass Filter
The highpassfilteris an 8-pole0.1dBchebeyshevactive filter thatcomprisesU410 andassociatedcomponents. The de-emphasis
is provided by resistor R451 and capacitor C471 . Receive audio is passed to U410 by Pin 4 of U411C where sub-audible tones
below 300Hz are attenuated. Mic audio is also fed into U410 via U411C (Pin 4) where sub-audible voice products below 300Hz
are also attenuated.
Mute (Squelch) Circuit
The mute circuit which is controlled by the output of U409 (micro) pin 77( 386EN ) is connected to pin 3 of Con 402 via R467
which mutes U7 (LM386) on the RF board. Pin 77 also controls Q408 and U402B which mutes the audio path to the RF board.
TX Audio and Filter Circuits
The TX audio from the internal mic (via U402A , C424 ) or external mic is fed into U401D and into U411C (Pin 3). The TX
audio is output on Pin 4 (U411C ) and into the high pass filter (U410) where sub-audible voice products are attenuated. The TX
audio output from U410 is fed into U404D &C which with associated parts form a mic amplifier and limiter. The output from
Pin 8 U404C is fed to RV402 (TX Modulation Level Adjust) and fed into U404A &B with associated parts to form a 3k low
pass filter. The output of U404A (Pin 1) is then fed into the Audio Mixer Circuit.
Analog Ground Supply
U406D supplies analog ground ( 2.0V ) to all operational amplifier circuits except for U405A and U405D .
Audio Mixer and Invertor
U405B is an audio mixer where mic audio and sub-audible tones combined. RV401 is used as a balance control. U405C is an
invertor, which when the appropriate links are opened or installed would adapt the digital board to the appropriated VHF and
UHF Scanning Handheld series models.
SWITCHABLE VHF AND UHF RADIO
CIRCUIT ANALYSIS
Page-12-
RF BOARD
VHF Transmitter
The Transmitter is comprised of:
1. Microphone Audio Circuit
2. Transmitter Stage and Harmonic Filter
3. Automatic Power Control
4. Frequency Synthesizer Circuit
Microphone Audio Circuit
Microphone audio from the digital board which has been amplified, pre-emphasized, and limitedis applied to the VCO via Con3
Pin 15.
Transmitter Stage and Harmonic Filter
The power amplifier contains transistors Q21 and Q22 , inductor L7 and capacitors C73 and C79 . When in the transmit mode
of operation, diode D2 is forward biased enabling the RF signal to pass to the input of U5 by C73 and L7 . U5 is the power
amplifier. The amplified RF signal passes through the stripline coupler and is fed to the harmonic low pass filter, comprising of
L12 to L15 and then to the antenna connector (ANT). The stripline coupler provides a sample of the RF signal for the automatic
power control. During transmit D6 is forward biased, inhibiting transmit signal power from being fed to the receiver circuitry.
Automatic Power Control
The automatic power control contains the stripline coupler, diode D4 and variable resistor VR1 , U4 , and two transistors Q19
and Q23. U4 forms a differential amplifier. The RF signal present in the coupler is rectified by D4 to produce a DC voltage. TX
5V is also applied to the input of U4 via the potential divider R34 and R35. The differential signal at output of U4 is passed to
Q19 and Q23 to produce a constant power output to the antenna connector (ANT). VR1 is used to adjust the RF power level.
Frequency Synthesizer Circuit
With data received from the EEPROM (U408), the frequency synthesizer circuit controls and produces the RF carrier frequency
for the transmitter during transmit and the local oscillator frequency for the receiver.
THE FREQUENCY SYNTHESIZER CIRCUIT IS COMPRISED OF:
1. RX and TX voltage controlled oscillator module.
2. Loop Filter
3. PLL Frequency Synthesizer & Dual Modules Prescaler
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CIRCUIT ANALYSIS
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VHF
Voltage Controlled Oscillator Module
The module produces carrier frequencies during transmit and local oscillator frequencies during receive. The module also has a
power line filter. Transistor Q308 is configured as a power supply ripple filter. The VCO comprises of transistors Q301 ,
Q302,Q303, and Q304, varactor D301 , D302 and adjustableinductorL301 and L303.Thesecomponentsarefiguredasacolpitts
oscillator. D301 and D303 produce a change in frequency with a change in DC voltage and is controlled by the phase detector
signal present at the anodes of D302 .
Receiver
The receive signal isroutedbackwardthroughthelowpassfilter,thenonwardtoPin1oftheHybridReceiverFront End Module.
A bandpass filter consisting of C800 - C812 and L800 - L803 is coupled to the base of Q800 which serves as the RF amplifier.
Diode D800 serves as protection from static and RF overload from nearby transmitters. The output of Q800 is then coupled to a
second bandpass filter consisting of C814 - C822 and L804 - L806 . The output of Pin 6 is then coupled to the doubly balanced
mixer U8. The receiver front end module is factory pre-tuned and requires no adjustment. Repair is effected by replacement of
the entire module of the proper banded module. These are 136 MHz to 162 MHz , and 148 MHz to 174 MHz. The receiver front
end module signal pins are as follows:
1. RF input
2. Input Ground
3. Ground
4. Receive +5V
5. Output Ground
6. RF Output
First Mixer
U8 is a Doubly Balanced Mixer (DBM) which provides the 45 MHz intermediate frequency output. The filtered frequency from
the front end module is coupled to Pin 4 of the DBM. The Local Oscillator from the VCO module, which runs 45 MHz higher
than the receive frequency, is coupled to Pin 1. The resultant IF output is output on Pin 5 of the D.BM.
The 45 MHz IF output is matched to the input of the 4 pole monolithic crystal filter by L20 , L18 , C113 , C114 , and C119 . The
crystal filter provides a bandwidth of + and - 7.5 kHz from the operating frequency, providing a high degree of spurious and
intermodulation protection. The output of the filter is impedance matched by L16 , C108, and C111 to the base of the post filter
IF amplifier Q24.
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CIRCUIT ANALYSIS
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Second Oscillator Mixer Limiter and FM Detector
The output of the Post Filter amplifier, Q24, is coupled via C118 to the input of Pin 16 U6. U6 is a monolithic single conversion
FM receiver, containing a mixer, the second local oscillator, limiter and quadrature detector. Crystal X1 44.545 MHz is used to
provide a resultant 455 kHz signal from the output of the second mixer. The mixer output is then routed to either CF1 ( 455E )
or CF2 ( 455HT ). These ceramic filters provide theadjacentchannelselectivityof 25 kHz or 12.5 kHz bandwidths. Respectively
selection of CF1 or CF2 is software controlled and programmable on a channel to channel basis. Control of the IF selectivity is
via Q32,D13,D14.The output of CF1 orCF2drivesahigh gain limiting amplifier, whichisinternally coupled to thequadrature
detector. The quadrature detector is also configurable for 25 kHz or 12.5 kHz channels spacings by the software control of Q31
and ( D12 ), which effectively parallels R86 with R85 to maintain audio output at the proper level for the bandwidth selected.
Squelch (Mute) Circuit
The Squelch circuit is an the input to the microprocessor which hascontrol of theaudio amplifier (LM386 enabled). The squelch
circuit consists of a 16kHz Band Pass Filter and a noise detector circuit.
16 kHz Band Pass Filter
The audio signal from Pin 9 of U6 ( MC3371 ) is filtered by a 16 kHz Band Pass filter consisting of L21 - L23, C128, C131 -
C134 . The noise in the IF passband is accepted and voice frequencies and their products are rejected. Any noise present at the
output of the filter is applied to the noise detector circuit via VR2 . VR2 is used to adjust the squelch circuit sensitivity and is
normally adjusted to produce a noise squelch opening sensitivity of 10 dB to 12 dB SINAD .
Noise Detector
The noisedetector,in conjunction with U6, consistsofQ25,Q26, Q27 , D8 , D11,TH1and theirassociatedbiasing components.
Noise fed from the output of VR2 is amplified by Q27 , then rectified by D11. This output is then buffered by Q26 and fed to
diode D8 , which controls Q25, providing a ground to the mute control Pin 14 of U6.
Low Pass Filter
A Low Pass Filter formed by C134 , C135 , L123 , and R82 removes any extraneous 455 kHz energy from the AF output of the
FM receiver chip. The audio is then routed to the digital PCB via Pin 15 of connector (Con4 ) for audio filtering and signaling
detection.
Speaker Audio Amplifier
After signal detection and audio filtering, the low level audio is returned to the RF PCB via Pin 14 of connector (Con4). This is
then routed to Pin 3 of U7 to provide speaker audio. U7 is disabled by a logic high applied to Q34 which in turn enables Q33,
applying 10.8 V to Pin 7 of U7 which forces output of U7 low.
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CIRCUIT ANALYSIS
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