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HANDBOOK OF INTERCOM
SYSTEMS ENGINEERING
FIRST EDITION
38109-977 Preliminary Rev. 4, 3/2002
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The Fine Print © The Handbook of Intercom Systems Engineering, first edition, Copyright 2000 by Telex Communica- tions, Inc. All rights reserved. Printed in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, electronic or mechanical, including photocopying and recording, or by any information storage or retrieval system without the prior written permission o
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TABLE OF CONTENTS Preface- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -3 About the Authors - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -5 Intercoms—An Overview- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -1 Introduction . . . . . . . .
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(Limitations of Each System). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 Design of Party-Line Intercom Systems - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -21 Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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(Connecting (Interfacing to Other Communications Systems)) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 (Some Practical Considerations) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 Introduction to Matrix Intercom Systems - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -45 Introduction . .
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Determining Intercom Needs - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 113 Conference Versus Point-to-Point Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Fixed vs. Mobile Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115 A General Overview . .
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Glossary - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -129 Index- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -151 v
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vi
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LIST OF FIGURES Simple Party-Line System - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1 Simple Matrix System - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2 Wireless Intercom Examples - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3 Example of Interfacing a TW System to a Matrix System - - - - - - - - - - - - - - - - - - - - 4 Complex Matrix Intercom System - - - - - - - - - - - - - - -
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A Comparison of Relative System Sizes - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -70 Separate Studios, Separate Intercom - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -71 Fixed Trunking - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -72 Intelligent Trunking - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -74 Cascaded Trunking - - - - - - - - - - - - - - - - - - - - - - - -
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C HAPTE R 0 C HAPTE R 0 C HAPTE R 0 C HAPT ER 0PREFACE Welcome to the Telex Communications, Inc. Handbook of Intercom Systems Engineering. The idea for this book came, as it does with many books and inventions, over drinks at a bar. A few of us “intercom types” were discussing our varied histories and experiences. We added up the years each of us had in the intercom system industry and between the four of us we hit the 75 year mark. Add the “rest of the gang” at Telex into that estimate and
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installation and support of intercom systems. In other words, we hope this book helps you get the absolute most out of your communications systems. Apart from the story of the bar and the trade show, there is another serious reason why we have written this book. Intercoms (in our opinion) are a neglected, underrated, taken for granted part of the technical world – they are not glamorous nor interesting. I have at times made the comment that intercom systems have a lot in common with toilets
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C HAPTE R 0 C HAPTE R 0 C HAPTE R 0 C HAPT ER 0ABOUT THE AUTHORS This handbook is the work of a number of past and present Telex employees, as well as, some outside experts (such as Stan Hubler). Among the contributors (in alphabetical order) are: Talal Aly-Youssef, Gene Behrend, Larry Benedict (contributor and editor), Rick Fisher, Stan Hubler, John King, Murray Porteous, Dave Richardson, Ralph Strader, and Tom Turkington. The credits for each chapter reflect the contribution of the primary
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6 Handbook of Intercom Systems Engineering
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C HAP T E R 1 C HAP TER 1INTERCOMS—AN OVERVIEW RALPH STRADER Introduction Intercom systems, by definition, may be comprised of many different types of intercoms and subsystems. The basic building blocks can be categorized into four basic types or elements: Party-Line Systems, Matrix Systems, Wireless Systems, and Accessories. Party-Line Systems Wired Party-Line systems are systems in which a number of participants are all involved in the same conversation. Think of the telephone extensions in
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Matrix Systems Wired Matrix systems are systems in which a large number of individuals have the ability to establish private individual conversations from point A to point B. Again, going back to the telephone system in your neighborhood, you, your next door neighbor, the pizza joint down the street and the local gas station are all connected to the same central office by wires from each location back to the telephone company. At any time, you can be talking to the gas station, while your n
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intercom system at some point. They can range from as simple as a single pair of units talking to one another, to a system in which 24 or more different portable units are dynamically switched between conversations. Figure 1.3 Wireless Intercom Examples Transmit to Beltpacks BTR-300 BTR-300 RadioCom Portable Transmit On 1 2 3 4 Ext Intercom Aux Audio Headset Headset Controls Controls Portable Station Connect Talk Gain O/M Power Push Twice to Latch Headset Volume Transmit to Base TR-300 TR-30
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Figure 1.4 Example of Interfacing a TW System to a Matrix System To connect a matrix intercom system to a Two-way radio system, a contact closure may be required to activate the radio transmitter. A GPI (General Purpose Interface) between the matrix and the base station of the radio can solve this problem easily. To do intelligent trunking between matrix systems, across campus or across the country, the audio and control signals between the matrices could be transported over fixed pairs of w
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Figure 1.5 Complex Matrix Intercom System MATRIX Audio IN, Audio OUT, Data Third Party NUM PL AUTO 1 2 3 SUST IFB ISO LISTEN DIR PROD RA PL01 IFB4 TD AD NEWS T1 TEL1 TEL2 FLOR CHYR ISO1 ISO2 AUD1 PHONE RELA 4 Y 5 6 COPY E-PANL 7 DISPLA 8 Y 9 Terminal CLEAR CALL MULT CLR 0 PGM FUNC Equipment Analog Keypanel Audio LAN / WAN Third Party Audio IN, Email Terminal Audio OUT, System Data Equipment News Third Party NUM PL AUTO 1 2 3 Computers LISTEN SUST IFB ISO PHONE DIR PROD RA PL01 IFB4 TD AD NEWS T1
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ISO Camera Isolate – This is not reserved strictly for the domain of cameras anymore. This is truly an isolate function, not unlike the action at a party of grabbing the arm of a fellow guest, dragging them off to a corner for a private conversation, and then returning them to their group. There are instances where it is necessary in an intercom system to establish a momentary private conversation with someone who may be talking and listening to a number of other people. The person who need
