Wescom, Inc.

Spencer L Hermanson

Albert G Nilssen

A DTMF signal receiver, for telephone systems, includes an amplifier with automatic gain control for receiving and amplifying DTMF and audio signals. A series of bandpass and notch filters receive the output from the amplifier for producing bandpass and notch outputs in response to the DTMF frequencies. A detector receives the bandpass output from each of the filters to produce a signal representing the presence or absence of a signal of each DTMF frequency in the amplifier output, and a DTMF decoder receives the signals from all such detectors and produces output signals in response to simultaneous detection of preselected pairs of DTMF frequencies. A voice guard circuit receives the notch output from the last filter in the series and compares the amplitude of that notch output with a threshold level to produce a disable signal whenever the amplitude of the notch output is greater than the threshold. This disable signal is supplied to the DTMF decoder for disabling the production of output signals by the decoder and thereby preventing the detection of invalid DTMF signals.

DTMF Signal receiver

A station-to-station supervision system for a telephone system has a dual tone multiple frequency (DTMF) signal generator connected to the transmit line at each subscriber station, and a standard audible signal generator is connected to the receive line at each subscriber station for generating dial tone, ringback tone, reorder tone and busy tone in response to supervisory DTMF signals. Control means associated with each subscriber station effect the generation of a dial tone disable DTMF signal from a calling station in response to the combination of an off-hook condition at the calling station and the absence of a DTMF signal from any other station in the system; a busy tone command DTMF signal from any given station in response to the combination of an address signal for that station and an off-hook condition at that station; and a ringback tone command DTMF signal from any given station in response to the combination of an address signal for that station and an on-hook condition at that station. The control means also generates a DTMF signal for terminating ringback tone at a calling station when a called station comes off-hook. The system also includes optional operating modes such as push-to-talk, conference calls, group calls, and all call.

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Mountain View, CA, United States of America

Spencer L Hermanson