Subscriber's circuit for four-wire-system local switch

Abstract From the Canadian patent

An subscriber's circuit for a four-wire-system local switch is provided with a tow-wire/four-wire hybrid circuit comprising: a two-wire/four-wire converter circuit; an incoming circuit device, connected between the converter circuit and a time-division switch section for amplifying an incoming voice current supplying a DC, current to a subscriber's telephone set and generating a subscriber's line signal of large amplitude such as a bell and howler signal by repeating the polarity reversal of the DC current and also an alarm signal by stepwise changing the duration and the frequency of the repetitive polarity reversal in response to digital command signals supplied thereto from the …