Telex 38109-977 manual + +

Figure 5.11 GPI/O Implemented PTT (Push-To-Talk)

2 Way Radio

Base Station

In Out PTT(n/o)

+- +-

GP I/O Interface

Relay Closes Upon

“Talk” Signal to

2 Way Radio

“PTT” (Push-to-Talk)

As mentioned earlier, TW systems are, by definition, two-wire (one pair) communications systems, having both talk and listen present at the same time on the same conductors. In order to connect a TW intercom system to a four-wire system an interface is required. This interface is known by a number of different names, including: hybrid, two-wire to four- wire converter, and system interface. Regardless of the name, the function is simple, although the technology is not.

80 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