Telex 38109-977 manual Some Definitions, Party-Line PL systems / Conference Line Intercom Systems

C H A P T E R

2

INTRODUCTION TO PARTY-LINE

INTERCOM SYSTEMS

STAN HUBLER

Introduction

Leading off this chapter, Some Definitions that may help you understand Party-Line intercoms terms (and buzz-words). Then, a Short History of Party-Line intercoms will be presented, leading into a discussion of Present Day Systems and Manufacturers. The System Components and Their Function will explore the main components of these systems and what they do. Then, How Each System Works shows how these system components are put together to make a functioning intercom and some examples of the different systems. Outstanding Features of Each System describes application areas and where each system is often marketed. Some important Limitations of Each System are described and a Summary closes this chapter.

Some Definitions

Party-Line (PL) systems / Conference Line Intercom Systems

A Party-Line system allows a group of people to intercommunicate. For example, one person can talk, while all the others on the bus or channel can hear. When the system is full duplex, anyone can talk and the rest can hear or interrupt the speaker at any time. The Party-Line and distributed matrix systems presently sold today are usually full duplex and are non-blocking, which means that access to the channel is immediate and there is no busy signal. Conversations on Party-Line systems are, in general, non-private. It is important to note that both two wire and four wire type systems support the Party-Line concept.

Two-Wire

A communications system where the path is the same for both talk and listen. In electrical pathways there are, in fact, two wires (one path). Two-wire systems can be two-wire balanced or two-wire unbalanced.

C h a p t e r 2 - I n t r o d u c t i o n t o P a r t y - L i n e I n t e r c o m S y s t e m s 7