Telex 38109-977 manual Outstanding Features of Each System, Cabling, Call Lights

Master Stations

These are multichannel stations. Some Master Stations are balanced (RTS™ TW Model 802/803) and require an interface (RTS™ TW Model 862 or 4012) to work with unbalanced channels. Master Stations can be configured to work with their respective systems with a minimum of interfacing. Master Stations have many functions which we go into to detail later.

Cabling

Usually the intercom system’s specifications are based on the use of 22 AWG microphone cable. Microphone cable of 22 gage measures 3 ohms per 100 feet or about 30 ohms per 1000 feet (round trip resistance). The wire table says 32 ohms per 1000 feet round trip, but the shield resistance is much lower than the wire resistance. The Audiocom® system uses both wires and the shield to transport DC so the calculations will be different for DC voltage drop versus distance.

Outstanding Features of Each System

The Audiocom® system is immune to noise and is a lower cost system. It is used in difficult environments, i.e.: churches, concerts, theaters, and sporting events.

The Clear-Com®system is robust, relatively lower in cost, and rental systems are readily available. It is often used for concerts, rock-n-roll tours, and in theaters. It is also used in remote trucks, uplink trucks, and low budget venues.

The RTS™ system is also very robust, reasonable in cost, and rental systems are readily available in most countries world wide. Because the RTS™ intercom has two channels per microphone cable, it is used where many channels are required, such as the Oscar and Emmy award shows. It is also used for events such as the Superbowl. Most larger TV trucks carry both a four-wire system and an RTS™ Party-Line system. These systems are interfaced together so the four-wire is used inside the truck and the RTS™ system is used outside the truck.

In addition to these features, most systems support extra features such as, “microphone kill” and “call light”. The microphone kill feature allows all microphones in a given channel to be switched off. In the case of Audiocom and RTS, the signal is an inaudible 24 kilohertz. In the case of Clear-Com, the power is interrupted for a long enough time to reset the microphones to off.

Call Lights

The Call Light Signal allows user stations to generate and display a visual signal for attention-getting and cueing purposes. The flashing light of the RTS™ and Audiocom® systems alerts the crew to put their headsets back on. The steady light of the Clear-Com®system can also be used for this purpose, however, it has another purpose: when the director holds the call light on, this is a standby signal. When the light goes off, this is the execute signal (raise/lower the scenery, follow spot on, et cetera). Call signals can also be used to key 2-way radios, sound alarms, and activate lighting controls. Audiocom® and RTS™ systems use an inaudible 20 kilohertz signal for the call signal; Clear-Com®systems use a DC voltage added to the audio signal. Telex manufactures a call signal detector / display (Model CIA-1000) which provides both a high visibility light and a relay closure when a call signal is sent. The CIA-1000 works with RTS™TW and Audiocom® systems. Clear-Com and other manufacturers also provide similar products. The company VMA supplies a bright strobe lamp that is triggered by the RTS™ system call signal. This

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 15