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Chapter 2 - Introduction to Party-Line Intercom Systems 17
3 This format allows louder and clearer communication. Party-Line intercoms can be
wired or wireless or both.
(System Components and Their Function)
1 The system components for most Party-Line intercoms consist of power supplies (or
main stations), user stations, interconnecting cable, headsets, panel microphones,
push-to-talk microphones, and a system termination.
2 The power supply (normally centralized) generates DC power for the entire system
(exception: self powered user stations).
3 The power supply usually includes the system termination.
4 User stations connect to the power supply and intercom line(s).
5 For a given channel, user stations are connected in parallel.
6 The interconnecting cable for most intercoms is standard microphone cable.
7 For the major three intercoms (and their clones) there are three wiring schemes.
8 Wireless intercoms usually include and interface to the wired systems.
9 Wired intercoms are mostly of the distributed amplifier kind.
10 Distributing the amplifiers allows for better performance and more features.
11 A single channel belt pack has an intercom line connector, a headset connector,
volume control, and a talk or microphone on/off switch. A two-channel belt pack
adds a channel selector or two talk switches and two volume controls.
12 A speaker station usually can be a headset or a speaker station.
13 Speaker stations add a power amplifier, speaker, and speaker on/off switching to the
headset station electronics.
14 Master Stations are multichannel and allow a director or lead person to have separate
conversations with various crews in any combination. Master Stations often have
many additional functions.
15 Dynamic microphones used with intercom stations usually range from 150 ohms to
500 ohms impedance. Electret microphones range from 1000 to 2000 ohms
impedance and require 1 to 5 volts DC excitation voltage.
16 Headphones range in impedance from 50 to 1000 ohms. For concerts and athletic
contests, 50 ohm headsets work better. The headphones should also have at least
20dB acoustic isolation for concerts and athletic contests.
17 The bridging impedance of each station should be 10,000 ohms or greater.
18 Since the power supply has a limited number of connectors, splitter boxes are needed
to expand the number of user stations in a system.
19 Both male and female XLR-4 connectors are used to connect the headset with the
user station. XLR-5 connectors are used for binaural headsets.
20 Some stations have loop through connectors to allow daisy chaining of stations.
(How Each System Works)
1 The stations use a voltage controller current source or similar electronics to apply
signal to the intercom line, yet exhibit a bridging impedance of 10,000 ohms or
greater.