Automatic audio signal detector for telephone voice lines - has resonant and broadband amplifiers which are coupled to voice lines

摘要

The automatic audio signal detector, for the voice lines in a telephone system has a resonant amplifier and there is a broadband amplifier which is connected to the voice lines of a calling subscriber circuit. Each amplifier is associated with a relay which is used to control the monitoring of the audio signal timing relay chain and a time switch. The advantage lies in the detector recognising an audio signal amidst noise arising e.g. from the presence of unwanted tones during selection, and the apparatus detects the signal despite obstructions e.g. engage tone in pre-selection stage.