Method and apparatus for detecting signalling and data signals on a telephone channel

摘要

The presence of such signals is detected each time the following detection condition is satisfied, namely: that, for the duration of a predetermined "prior activity" period the amplitude of the signal on the telephone channel exceeds a threshold level while successive maximum values taken at short time intervals remain fairly constant in level. Apparatus for performing the method comprises a threshold level comparator (10) and a difference comparator (11) which control a detector (50) followed by a holdover circuit (60). The invention is particularly applicable to inhibiting echo suppressor circuits during telephone signalling or data transfer by telephone line.