The CM-TBU line-powered telephone balance unit is compatible with all analogue direct exchange lines and provides a 4-wire communications system to interface with the telephone network. The high degree of separation between send and receive signals makes it suitable for use in telephone IFB (interrupted foldback) applications and the high drive capacity at the 4-wire output enables a presenter’s earpiece to be connected directly to the unit without an external amplifier. This extremely compact unit is powered from the telephone line and provides an interface to a 4-wire circuit with separate level control of send and receive signals. Optimum rejection of the input signal on the 4-wire output is achieved in a bridge circuit by adjusting three elements (NULL, R-BAL and C-BAL) via potentiometers which simulate the complex line impedance. 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.
Product Features
Isolated, full-duplex 4-wire interface to direct non-digital telephone exchange lines.
Line powered, requiring no battery or external power.
Simple optimization of sidetone rejection with any country’s telephone system.
LEDs indicating ‘Ring’, ‘Line Hold’ and ‘Limit’ conditions.
Input level control with line-sensing limiter and limit indicator.
High drive output with level control for direct feed to presenter’s earpiece, etc.
Loop-through RJ11 line sockets provide universal connection to line and telephone set.
Connection to the telephone set is maintained while the unit is in use.
Small, rugged aluminium case.
Typical Applications
Talkback applications, e.g. to get cue feed to a remote presenter from a distant studio, hospital/community radio talkshows, house of worship remote listen & contribution to service.
Product Category
Telephone Talkback
Technical Specifications
4-Wire Input
Input Impedance: 10kΩ, transformer coupled
Input Connector: 3 pin XLR female connector
Input Level Range: -12dBU to +4dBU before limiting when connected to an average line
4-Wire Output
Output Impedance: 150Ω, transformer coupled
Output Connector: 3 pin XLR male connector
Output Level Range: -6dBU to +6dBU, for average line level
Sidetone Rejection: 30dB to 40dB average, depending on line characteristics
2-Wire
Off Hook Voltage: 6V minimum
2 Wire Connectors: RJ11 socket - line
2 Wire Connectors: RJ11 socket - handset
Front Panel Operational Controls
Line Connect: Push button with indicator
Send Level: Small rotary control
Receive Level: Large rotary control
Null Balance: Recessed preset potentiometer
R Balance: Recessed preset potentiometer
C Balance: Recessed preset potentiometer
Ring LED: Indicates incoming ringing
Limit LED: Indicates limiter active
On LED: Indicates connection to the telephone line
