The TBU (Telephone Balance Unit) provide high degree of separation between send and receive signals, enabling 4-wires communications system to interface with the telephone network.
In telephone IFB applications, the high drive capacity at the 4-wires output, enables a presenter’s earpiece to be connected directly to the unit without an external amplifier.
The unit is line powered.
Isolated, full-duplex 4-wires interface to
non-digital telephone direct exchange lines.
Simple optimization of sidetone rejection.
LED’s indicate “ring” and “off hook”
Input level control.
High drive output with level control.
Loop-through telephone line sockets
- Connection to the telephone set is maintained
while the unit is in use
This unit is powered from the telephone line and provides an
interface to a 4-wires circuit with separate level control of send
and receive signals.
Optimum rejection of the input signal on the 4-wires output is
achieved by adjusting SIDETONE NULL trimmer.
This can be used to compensate for local line variations or to adapt
to the telephone systems of other countries, where line
characteristics may differ.
To enable communication between the 4-wires circuit and the
telephone network, the 4-wires an line connections are made to the
unit and the “hook” switch is pressed to power the unit from the
This will be indicated by the ON LED, and can either be done after
an outgoing call has been dialed on a telephone set connected to the
unit, or to answer an incoming call after RING LED is seen flash (a
telephone set is not required for incoming calls unless an audible
ring is required).
If the sidetone level at the 4-wires output is found to be
excessive, the outgoing signal level should be reduced or the
balance controls adjusted to minimize it.
To ensure compatibility with all systems, a switch is provided to
select either the inner or outer pair of conductors on the RJ11