Evaluation of echo suppression in video teleconferencing via the communications technology satellite

The Lister Hill National Center for Biomedical Communications encountered an echo problem during the operation of its six station network which provided full-duplex channels via the Communications Technology Satellite. The mechanisms causing echo are discussed, followed by a brief outline of technical approaches to its solution: simple loss insertion, echo suppressor, and echo canceller. The echo suppressor, being an off-the-shelf item, is the device selected to solve the problem. The problems encountered with the echo suppressor, the modifications attempted, and the solution finally adopted which involved using the echo suppressor in cascade with a voice gate amplifier are described.