| 摘要 |
PCT No. PCT/SE90/00051 Sec. 371 Date Sep. 23, 1991 Sec. 102(e) Date Sep. 23, 1991 PCT Filed Jan. 24, 1990 PCT Pub. No. WO90/09067 PCT Pub. Date Aug. 9, 1990.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. |
