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42 Handbook of Intercom Systems Engineering
9 A training system usually consists of a station for the instructor and multiple,
independently addressable student stations.
10In a large system for television production, additional accessory equipment allow
expanding the Party-Line into 12 or more Party-Line channels, isolated camera
channels, IFB capable stations, and wireless intercoms.
(The IFB System (One Way Communications System))
1 IFB is an acronym for Interrupted FeedBack, Interrupted FoldBack, or Interrupted
Return Feed (also known as IRF).
2 An IFB system allows people running the show, such as director, producer, and mixer
to talk to the talent or actors directly. The talent may receive cues, additional
information, or hear other talent in other locations to be able to talk with them.
3 The IFB system consists of a 1) a hot mic feed from a director, producer, et cetera, 2) a
control panel, 3) connecting cables, 4) talent station, 5) talent headset or earset. Some
IFB systems are wireless. This requires some different equipment, and the wireless
feature eliminates the connecting cables.
4 IFB systems are often required to operate over large systems, as much as a mile.
(Connecting (Interfacing to Other Communications Systems))
1 Interfacing is connecting two separate communications together or not directly
communications to the Party-Line.
2 One modern interface requirement is two connect a two-wire Party-Line system to a
four-wire intercom system.
3 Interfaces often can compensate for system to system: a) level differences, b) mode
differences, c) impedance differences, and can translate call light and other data signals
into suitable formats.
4 Interfacing to various television cameras is often challenging and may require extra
equipment and extra efforts.
5 There are three tasks to interfacing: mode conversion, level changing, and signal / data
conversion.
(Some Practical Considerations)
1 A too long headset cable may cause feedback or crosstalk problems.
2 Low impedance headphones, in general are louder and cause the user station to draw
more current. Higher impedance headphones lower current drain but may not be loud
enough for use during concerts or athletic contests.
3 Accidental connection of the shield in a microphone cable to earth grounded objects
may cause hum and noise in the intercom system.
4 Taping or fastening metal intercom stations to metal structures may introduce into the
Party-Line intercom system.
5 Cabling in poor condition may introduce noise / intermittent operation into a system.
6 It may be necessary to convert the intercom audio to a balanced configuration to cover
long distances or to overcome strong interference from adjacent cables.
7 Extending the range of the Party-Line intercom may require using heavier gage cables,
or using special schemes of “local powering” the remote user station.