Sonifex CM-TBU Line Powered Telephone Balance UnitThe 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. 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 countrys telephone system. LEDs indicating Ring, Line Hold and