Telex 38109-977 manual

(now often called HTs or Handie-Talkies) have higher operating power which affords substantially increased operating range of over a mile or more in some cases. This range can be increased to cover an entire city by the use of repeater stations located at the top of centrally located buildings.

Two-way radios did not, however, do as well for the rigors of live television production. In live TV, the restrictive nature of HTs was only too evident. First, HTs utilize a half-duplex communication scheme. Half-duplex means that while there is bi-directional conversation, only one user may communicate at a time and all other users must listen until the person who is communicating is finished. During setup this does not pose a huge problem, but during a show, when seconds can seem like hours, this can be a real problem. Imagine a cameraman is transmitting over a half-duplex HT system, while the director is trying to take a new shot or make some other time-critical change. Obviously, a half-duplex system would never do.

Soon after it became apparent that a half-duplex communications system would never satisfy the needs of on-air production, a vast array of new HT-based system configurations emerged. The greatest of these utilized two HTs on each user and multiple base station units in a complex repeater configuration. An interface box allowed users to wear one headset that fed both radios at once. While achieving some of the functionality of the most basic modern day wireless intercom, the system was bulky, heavy and unreliable due to the numerous wires and complexity of setup. While this system was much closer, it still did not offer communications professionals the robust functionality and reliability they needed for day-to-day operations.

The next generation of wireless intercoms to hit the scene was truly a breakthrough. It eliminated much of the complex wiring and minimized the equipment the user was forced to wear. The system consisted of a base station and multiple user beltpack pairs. In the base station there was a single transmitter and multiple receivers (one for each wireless user). The audio coming from each receiver was put on a single intercom channel or audio bus, and was fed to the transmitter as well as an external intercom line. The transmitter was a low power, always on unit that maintained constant outgoing information to all wireless users. See Figure 6.1.

86 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