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Apparatus for selectively alerting party line subscribers

  • US 4,723,271 A
  • Filed: 10/15/1985
  • Issued: 02/02/1988
  • Est. Priority Date: 10/15/1985
  • Status: Expired due to Term
First Claim
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1. An apparatus for selectively alerting subscribers in a party line system having at least three wires comprising:

  • DC bias detection means for detecting when a signal received by a first line is DC biased in a first direction with respect to both a signal received by a second line and a signal received by a third line, each of said first, second and third lines being coupled to one of said three wires of said party line system,AC signal detection means detecting when an AC signal of predetermined frequency is present on one of said first and second lines,an incoming line being coupled to one of said three wires of the party line system,an outgoing line being coupled to subscriber alerting equipment so as to transmit a subscriber alerting signal to said equipment, andswitch means optically isolated from said DC bias detection means and said AC signal detection means for coupling the incoming line to the outgoing line when the DC bias detection means and the AC signal detection means detect the signals specified.

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