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Transparent secondary information transmission system for an information transmission system

  • US 4,493,948 A
  • Filed: 06/27/1983
  • Issued: 01/15/1985
  • Est. Priority Date: 06/27/1983
  • Status: Expired due to Fees
First Claim
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1. A condition monitoring system adapted to be connected in a telephone system comprising circuit means for monitoring at least one condition at a first location in the telephone system and providing a first signal representative of the condition, first means adapted to be coupled to a pair of ring and tip lines of the telephone system at the first location and to earth ground for transmitting substantially said first signal simultaneously on both said ring and tip lines such that substantially no signal is produced across said ring and tip lines from transmission of said first signal on both said ring and tip lines, second means adapted to be coupled to the ring and tip lines at the second location and earth ground for transmitting substantially a second signal simultaneously on both said ring and tip lines such that substantially no signal is produced across said ring and tip lines from transmission of said second signal on both said ring and tip lines and for receiving said first signal at said second location in the telephone system and generating a signal responsive to a predetermined condition of said first signal, said first means further comprising balanced modulator/demodulator means for receiving said second signal from said second location transmitted on said ring and tip lines, said first balanced modulator/demodulator means further comprising modulator means for converting said first signal into a modulated signal, amplifier means for increasing the amplitude of said modulated signal so as to produce an amplified modulated signal, said amplified modulated signal present on an output of said amplifier means, said output coupled to telephone line coupling means, said telephone line coupling means comprising resistor/capacitor circuit means coupled to both said ring and tip lines of said telephone system for coupling said amplified modulated signal to both said ring and tip lines and further comprising means for adjusting said amplified modulated signal so that said amplified modulated signal is substantially undetected across said ring and tip lines but may be detected across either of said ring and tip lines and earth ground, whereby said first means for transmitting is substantially transparent to said telephone system, and further comprising duplexer means coupled to the output of said amplifier means and to said telephone line coupling means, said duplexer means having an output coupled to filter means, said duplexer means allowing said second signal received by said telephone line coupling means to be coupled to said filter means, and further comprising demodulator means for converting said received signals into a demodulated signal, said filter means coupled to said demodulator means, said demodulated signal coupled to said circuit means for controlling said circuit means.

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