Telex 38109-977 manual System Components and Their Function

sound powered system, but we do not discuss it here. Present day Party-Line intercom systems may be wired or wireless or both.

System Components and Their Function

The system components for most Party-Line intercoms consist of power supplies (or master stations), user stations (e.g. belt packs, speaker stations, main stations, etc.), interconnecting cable, headsets, panel microphones, push-to-talk microphones, and a system termination.

The power supply (which is normally centralized) generates the DC power for the entire system (with the exception of self powered user stations). The power supply usually includes system termination for the audio channel, 200 ohms for RTS and Clear-Com, and 300 ohms for Audiocom. This may be as simple as a capacitor and resistor in a series, or, an electronic termination, which is integrated into the power supply voltage regulator.

The user station connects to the power supply and intercom line. The human user connects to the user station via a headset or loudspeaker and microphone or some combination. For a given channel or channels the user stations are connected to each other in parallel.

The interconnecting cable for most intercoms is standard microphone cable with three pin XLR type connectors. The female XLR connects towards the power supply and the male XLR plugs into the user station. This polarity was chosen to prevent putting DC power onto audio microphones which also use this type cable. There are at least two exceptions to the use of microphone cable: the RTS™ TW master stations connect audio with unshielded pairs (12 of the 25 pair in a cable). Another exception is where a twisted pair is the only connection between two points. The RTS™ TW user stations can connect directly to a twisted pair, while other user stations need adapters of one kind or another, and power may have to be supplied at either end.

The wired systems are of three wiring configurations: 1) separate power, audio, and return

conductors (example: Clear-Com), 2)an audio pair which includes phantom power and a

common (example: Audiocom), and 3) a conductor that contains one channel and power, a

conductor that contains audio with- or without power, and a return (example: RTS™ TWTW intercom system).

10 H a n d b o o k o f I n t e r c o m S y s t e m s E n g i n e e r i n g