Toa EXES-6000, Operating And Troubleshooting

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1. Hands-free System
1-1. Basic Principle of the Hands-free System
Fig. 1 shows a basic principle of the hands-free
system that permits duplex conversation to be
made between the calling and called parties
without using their hands to lift their station
handsets.
Feedback produced between the microphone and
the speaker by the following reasons, however,
makes it impossible for the system to be in actual
use:
a) Both the speaker and microphone are housed
in a small case, causing them to be located in
close proximity to each other.
b) Speaker audio output level is high.
c) Microphone is very sensitive.
Fig.1 Hands-free System
1-2. Voice Switch
To make the hands-free half-duplex conversation
possible by preventing occurrence of such
feedback problem, Toa EXES-6000 system uses
voice switch in its exchange that is able to detect
signal strength information from both lines and to
automatically select the speech line of higher
signal level, while disconnecting another speech
line of the lower signal level. See Fig. 2.
Fig.2 Principle of the Voice Switch
I. BASIC ITEMS