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Chapter 2 - Introduction to Party-Line Intercom Systems 11
The wireless systems usually include an interface to the wired systems. Principal
manufacturers include Telex Communications, Vega (now part of Clear-Com), and HME.
We will go into further detail on wireless systems in a later chapter of this manual.
Wired intercoms are mostly of the distributed amplifier kind. The distributed amplifier is
built into a User Station. User stations come in various packages and are of three kinds:
headset, speaker-microphone, or both. The various packages include a belt pack (worn on
the users belt, and of the headset kind), console mount (headset or speaker-microphone),
rack mount (headset or speaker-microphone), desk mount (portable speaker station), wall
mount (headset or speaker-microphone), and console/rack mount Master Station/Main
Station (details later). The distributed amplifier concept allows each user to adjust his/hers
own listening level. The user station also includes a microphone amplifier, a line
amplifier/buffer, volume control(s), talk switch(es). Some user stations also may have a
Call light, status indicators, and a channel selector. The microphone may be in the headset,
fastened to or plugged into a speaker station, in a handset, or in a push-to-talk hand held
unit.
Belt Pack Headset User Station Functional Description
A typical single channel belt pack headset user station has the following connectors:
Intercom Line (XLR-3) and a Headset Connector (XLR-4).
The station has the following controls:
Microphone ON/OFF (sometimes called a TALK switch), and a headset Volume Control.
It may also have a Call Lamp and a Call Lamp Send button. Examples of this station are an
RTS
™
BP318 single channel belt pack, or an Audiocom
®
BP1002, or a Clear-Com
®
RS-
501.
A typical two channel headset belt pack user station adds a channel selector switch to the
above. Examples RTS
™
BP351, Clear-Com
®
RS-502, Audiocom
®
BP2002
Table 2.2
Intercom connector wiring by various manufacturers.
Clear-Com
Pin # Function
1 Common for Audio, Power, &
Shield
2 DC power: 30 volts nominal
3 Unbalanced Audio
Audiocom
Pin # Function
1 Common for Audio, Power, &
Shield
2Audio + DC Power
3Audio + DC Power
RTS TW
Pin # Function
1 Common for Audio, Power &
Shield
2 Channel 1 Audio + DC Power
3 Channel 2 Audio