Stromberg-carlson Corporation

Morris A Suntop

Uno Randmere

A loudspeaking telephone system including voice switching is disclosed. The system is bistably voice controlled by inversely regulating the impedances of variolossers in the transmit and receive channels respectively. Further provision is made for switching additional impedance in parallel with each variolosser control to provide for a loud and a soft receiving mode. Hysteresis is added to the bistable control by the summation of receive and transmit signals across a plurality of unequal impedances that form part of a novel input control means. Circuitry forming the input control means also includes noise guard means useful in discriminating between ambient noise signals and syllabic speech signals. The noise guard circuit discriminates between noise signals and speech signals by producing an output whose amplitude is substantially related to ambient noise conditions while the noise guard circuit generally is not responsive to rapidly fluctuating voice signals. The output of the noise guard circuit is then summed with the transmit and receive signals across unequal impedances to prevent seizure of the bistable control by ambient noise.

Loudspeaking telephone hysteresis and ambient noise control

An interface circuit is disclosed for ground starting central office trunks connected via a station carrier system to a plurality of PBX subscriber terminals. The interface circuit extends ground start signals between central office sensing means and subscriber terminal control means over the high frequency transmission cable of a multiple-channel station carrier system. Associated with each of the plurality of multiple-channel units that interface central office terminal trunks to the carrier system are ground start sensing means multiply connected to ground start common circuitry. The ground start common circuit interprets signals from the ground start sensing means as to which of the voice frequency connecting pairs indicates a signal ground and subsequently forwards this information in the form of modulated intelligence on a discrete carrier over the high frequency transmission highway. At the PBX terminal, ground start control means are used to demodulate the transmitted intelligence and selectively control the subscriber terminal for voice frequency connection or battery reversal. The ground start control circuitry further includes means to initiate a ground start signal through the station carrier channel circuitry that is recognized by the ground start sensing means and used to alert the corresponding central office trunk of such a condition.

PBX ground start trunk interface for station carrier systems

A telephone system comprises a non-loaded, non-equalized cable interconnecting a pair of communication terminals so that audio signals are translated in one direction and modulated carrier signals are translated in the other direction. A direct current bypass circuit is provided at each terminal to allow the transmission of direct current supervisory signals and battery potential over the non-loaded, non-equalized cable.

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Rochester, NY, United States of America

Morris A Suntop