Telex 38109-977 manual Interfacing Practice, Problems in Interfacing to Cameras

Interfacing Practice

Interfacing Television Camera Intercom Systems to TW Systems

General Camera Configuration Information for Television Cameras (except ENG units)

Television cameras used in broadcast and industry usually have two parts: a camera head and a camera control unit (CCU). The camera head assembly usually contains the lens equipment, camera electronics, and triax adapter (if used). The CCU contains additional electronics for processing video, the other end of the triax adapter, an interface for microphone audio, and the intercom interface. The intercom interface usually incorporates switches and electronics so that the intercom can be two-wire or four-wire.

The Problems in Interfacing to Cameras

There are two problem areas in television camera intercoms:

1The electronics in the camera head.

2The intercom interfacing electronics at the CCU.

Some possible problems with the camera head intercom electronics are as follows:

•Inadequate headphone drive (Not loud enough for athletic contests and studio shows)

•No limiter in the microphone preamplifier (level variations are too much)

•The headphone and the microphone share a common circuit return conductor (headphones oscillate when volume is turned up)

•The Triax Adapter / electronics does not give the camera intercom enough headroom, so there is a trade-off between signal clipping and signal to noise ratio.

•The microphone on/off switch does not disconnect the microphone preamplifier thus adding noise to the system.

•Some possible problems with the CCU intercom interface electronics are:

•An earth ground is applied to the wiring usually in two-wire mode (causes hum loops in the system)

•The four-wire input to the camera is not bridging impedance

•The two wire “RTS0153 Systems compatible” interface loads the line

•No safety capacitors are installed in the CCU, thus causing burnt transformers if connected to the intercom line

Alternatives for Interfacing to Television Cameras

1Bypass the camera, tape a microphone cable to the camera cable, and plug a TW belt pack in at the end.

2Use the existing camera intercom, interface it to the TW system with a Model SSA324 or SSA424 interface (if camera intercom is four-wire).

3In multi-core connected cameras, use the camera wiring to allow a TW belt pack to be plugged into the camera head. This allows the camera operator to use a portable User Station mounted on his belt or attached to the camera body. (

Note: This requires significant modification to the camera head and CCU)

36 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