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Chapter 5 - Design of Matrix Intercom Systems 81
Figure 5.12
TW to Matrix Interface
The hybrid, in Figure 5.12, acts as a “traffic cop” allowing the talk signal from the matrix
to be applied to the bi-directional TW line while blocking its return when the talk signal
from the TW is presented to the matrix. The effect of the blocking is termed “nulling”, as it
cancels of the return signal. The effectiveness of the cancellation is driven by many
factors. Hybrids are generally available from many sources, including intercom
manufacturers, Gentner, Telos, and others. Telex has two models available, the RTS
™
SSA-324, and the RTS
™
SSA-424. Both units are suitable for most applications. The
primary difference is the SSA-424 is digital and auto-nulling, eliminating the need for
manual setup and calibration.
Software Considerations
Until now, we have concentrated on the physical and hardware issues for a matrix
intercom system. As noted earlier, the intercom matrix itself is a matrix mixer, which is
capable of mixing any combination of inputs to any output. A 50-port system is literally a
50-input by 50-output bus digital mixer. Firmware and software are what turns this digital
mixer into an intercom system.
For the following discussion, it is helpful to understand the different roles played by the
system firmware and software in a matrix intercom system. As system architectures vary,
and some information is proprietary to each manufacturer, the information being presented