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80 Handbook of Intercom Systems Engineering
Figure 5.11
GPI/O Implemented 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.
Relay Closes Upon
“Talk” Signal to
2 Way Radio
“PTT” (Push-to-Talk)
GP I/O Interface
2 Way Radio
Base Station
Out
In
PTT(n/o)
+
-
+
-