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Apparatus for discriminating television signal

  • US 4,283,740 A
  • Filed: 11/08/1979
  • Issued: 08/11/1981
  • Est. Priority Date: 11/18/1978
  • Status: Expired due to Term
First Claim
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1. In an apparatus for discriminating a television signal for use in a pay television system in which a scrambled television signal is transmitted from a broadcasting station and specified subscribers view by restoring the received scrambled television signal, said apparatus comprising a first sync separator connected to an output of a demodulator, a second sync separator connected to said output of said demodulator through an invertor, and a television signal discriminating control circuit means coupled to said first and second sync separators for determining whether the received television signal is from one of a pay television broadcasting station and a normal television broadcasting station in accordance with output signals from said first and second sync separators and for supplying restored television signals to a television receiver, wherein the improvement comprises:

  • enabling control circuit means coupled to said first and second sync separators for controlling the outputs of said first and second sync separators and for controlling the input impedance of said first sync separator; and

    initializing circuit means coupled between said signal discriminating control circuit means and said enabling control circuit means for controlling said enabling control circuit means;

    wherein said enabling control circuit means initially supplies an output from said first sync separator to said signal discriminating control circuit means; and

    wherein, if said signal discriminating control circuit means is not satisfied with said output from said first sync separator, said enabling control circuit means supplies an output from said second sync separator to said signal discriminating circuit means, and said enabling control circuit means changes the input impedance of said first sync separator so as to place said first sync separator in a half-enabling state.

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