Call signal detecting device

Abstract From the Canadian patent

In a facsimile communication system a device for connection to a, telephone line through which unsounding and sounding a.c. call signals of different frequencies may be received, to a facsimile machine; and to a telephone set, the device being adapted to detect and discriminate between the sounding and unsounding call signals. The device comprises first binarizer means for converting any a.c. signal received over the telephone line into a signal having two binary levels; second binarizer means adapted to be unresponsive to unsounding call signals whilst converting a sounding call signal into a signal having two binary levels; and selector means connected to receive the outputs of the first …