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ELECTRONIC COMMUNICATION APPARATUS FOR SELECTIVELY DISTRIBUTING SUPPLEMENTARY PRIVATE PROGRAMMING

  • US 3,730,980 A
  • Filed: 05/24/1971
  • Issued: 05/01/1973
  • Est. Priority Date: 05/24/1971
  • Status: Expired due to Term
First Claim
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1. In combination in a television communication system for propagating private supplementary television signals;

  • means for supplying at least one private program having an inverted modulation spectrum with a sound carrier lower in frequency than the picture carrier and a vestigial upper video side band, means for distributing said private television program, and converter means coupled to said distributing means for recovering said private programs, said converter means includIng heterodyning means for reversing the modulation spectrum of said private program distributed by said distribution means, said heterodyning means including mixer means and local oscillator means for providing an output signal higher in frequency than the highest frequency of said distributed private television programs for inverting the modulation spectrum of said private programs and for shifting the inverted spectrum in frequency, wherein said private program supplying means including means for supplying two private programs, each having an inverted modulation spectrum and a vestigial upper video side band, said programs having all frequencies components thereof in the range 88-174 mc, said two spectra having corresponding parts thereof separated by the interchannel frequency difference between two commercial television channels.

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