ECHO CANCELLER WITH ADAPTIVE VOICE SWITCH ATTENUATION

This invention relates to an echo canceller (EC) such as for use in a full duplex radio. The echo canceller comprises: an output path (10) for outputting desired signals; an input path (12) for receiving desired signals together with undesired echos from the output path; an adaptive filter (14) for filtering signals on the input path; measuring means (18) for measuring echo attenuation by the adaptive filter; a variable attenuator (15) for attenuating signals on the input path; control means (16) for controlling the variable attenuator to provide a degree of attenuation dependent on the difference between attenuation measured by the measuring means and a predetermined desired attenuation. The echo canceller is particularly useful in any system having large transmission delays like GSM cellular radio telephone system.