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Method and apparatus for preventing external detection of signal information
| Details |
Inventors: Lindholm, Per;
Assignee: Cominvest Research AB (Stockholm, SE)
Primary Examiner: Cangialosi; Salvatore
Assistant Examiner:
Attorney, Agent or Firm: Cushman Darby & Cushman
In a method and an apparatus for preventing external detection of the signal information in video signals occurring in, and being emitted from, video signal circuits in a display unit (A, A'), or a similar unit, and comprising substantially consecutive frame or field signals, each consisting of substantially consecutive line signals, a phantom signal in the form of at least one pseudo-random bit signal sequence with properties similar to those of the video signals is emitted in addition to the video signals. A generator (C) for generating the phantom signal is connected to an external power supply line (F) to the unit (A, A') containing the video signal circuits, for output of the phantom signal on this line. By means of a control unit, the bit frequencies of the pseudo-random bit signal sequence/sequences are varied. Furthermore, the pseudo-random bit signal sequence/sequences are formed of a number of part signal sequences wtih a duration varying from one frame or field period to another. |
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DETAILED DESCRIPTION I claim: 1.
A method for preventing external detection of signal information in video signals comprising steps of: a) emitting video signals containing a bit signal sequence from a video circuit; b) generating a phantom signal with at least one pseudo-random bit signal sequence and having properties similar to the bit signal sequence of the video signals emitted from the video circuit; c) varying bit frequencies of the pseudo-random bit signal sequence; d) emitting the phantom signal in addition to the video signals via electromagnetic waves; and e) supplying the phantom signal to an external power supply line connected to the video circuit.
2.
A method as in claim 1, wherein the pseudo-random bit signal sequence has bit frequencies different from, but of the same order of magnitude as a pixel frequency of the video signal.
3.
A method as in claim 2, wherein the bit frequencies are varied at substantially the same magnitude as a line frequency of the video signal.
4.
A method as in claim 3, wherein the pseudo-random bit signal sequence is given a duration corresponding to a frame or field period time of the video signals, and an ensemble average value differing from zero, the pseudo-random bit signal sequence being formed of a number of partial pseudo-random bit signal sequences, characterized in that the duration of the partial pseudo-random bit signal sequences are varied within each frame or field period.
5.
A method as in claim 4, wherein the pseudo-random bit signal sequence includes a number of partial pseudo-random bit signal sequences with a duration varying from one frame or field period to another.
6.
A method as in claim 5, further comprising the step of: combining a plurality of pseudo-random bit signal sequences before either step d or e.
7.
A method as in claim 1, wherein the pseudo-random unit signal sequence has bit frequencies which are varied at substantially the same magnitude as a line frequency of the video signal.
8.
A method as in claim 7, wherein the pseudo-random bit signal sequence is given a duration corresponding to a frame or field period time of the video signals, and an ensemble average value differing from zero, the pseudo-random bit signal sequence being formed of a number of pseudo-random bit signal partial signal sequences, characterized in that the duration of the partial pseudo-random bit signal sequences are varied within each frame or field period
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Telecommunications 
