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Apparatus for transmitting information via telephone lines

  • US 4,521,643 A
  • Filed: 02/18/1983
  • Issued: 06/04/1985
  • Est. Priority Date: 01/10/1983
  • Status: Expired due to Term
First Claim
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1. Apparatus comprising a telephone subscriber line connected at a first end to a telephone and at a second end to a central office, means for transmitting information via the line when the telephone is on-hook, means for applying a pilot tone to the line at the first end when the telephone is off-hook, means coupled to the line at the first end for detecting the presence of ringing signals on the line, means for selecting one of two frequencies of the pilot tone applied to the line when the telephone goes off-hook in dependence upon the detection of the presence of ringing signals, and means for monitoring the pilot tone at the second end of the line.

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