Pbx ground start trunk interface for station carrier systems

Abstract

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.