Instruction manual

ACU-1000 Operations Manual
Interoperability Now 1-7
1.4.1.2 Radio-to-Telephone Cross-connections
Figure 1-3 Basic Phone Patch
Figure 1-3 shows a basic connection between a 4-wire device (such as a radio) and a 2-wire
device (such as a telephone line). 2-wire devices carry audio in both directions,
simultaneously, on a single pair of wires. An interface (commonly referred to as Phone Patch)
is required between these two disparate devices. In actuality, the phone patch 2-wire
connection does not interface directly to a telephone, but instead to the telephone system. The
phone patch would most likely be connected to a phone jack on the wall by a standard
telephone cable with RJ-11 connectors. To talk over the radio via the phone patch, you would
use your telephone to call the number associated with that phone jack on the wall.
With most standard 2-wire devices (such as a telephone), there are no accompanying control
signals such as PTT or COR. Because of its ability to carry both send & receive audio at the
same time, these control signals do not benefit the telephone system. Therefore a 2-wire to 4-
wire radio connection requires that a VOX function be provided to derive the COR signal from
the incoming phone line audio and supply the associated PTT output signal to the radio. The
VOX (Voice Operated Xmit) triggers the PTT when a large enough signal is detected coming
from the telephone system to indicate that the end-user is talking.
A VOX output is activated by the detection of audio that exceeds the set
VOX threshold.
A Phone Patch interfaces the 2-wire telephone system to a 4-wire radio.