Abstract: A cable card having increased cable connector density is provided. The cable card has a non-planar surface and, therefore, more surface area than a planar cable card having the same outside dimensions. The increased surface area of the non-planar surface permits more connectors of a given size to be located on the cable card.

Abstract: Video signal lines are added to or omitted from the ends of individual fields of a video signal to produce a modified video signal whose field length varies at a slow rate. The modified video signal can be broadcast and received by conventional television equipment, normal television reception and viewing being not noticeably affected by the variable field length. However, recording of the modified video signal is inhibited because the field length is not constant. The modified video signal is produced by directly modifying the scanning of televising equipment, or by storing the lines of the video signal in a store and reading them in a controlled manner therefrom. A decoder, for producing a constant field length video signal from the modified video signal, is also disclosed.

Abstract: Speech signals are optically coupled from a transmitter to a receiver using low duty-cycle infrared pulses. A conditioning circuit converts an a.c. input signal to be transmitted into a unipolar signal, whose magnitude controls the frequency of an oscillator which determines the frequency of the infrared pulses. In the receiver the detected pulses are low-pass filtered in a voice-band filter the output of which is coupled to a telephone line and/or a loudspeaker. A plurality of similar transmitters can be provided to enable signals from an arbitrary number of people to be coupled to a common receiver.

Abstract: A scrambler scrambles a video signal by replacing its vertical intervals with dummy video signal lines, and separately providing information relating to the timing of the replaced vertical intervals. This information is encoded using an encryption key and is distributed with the scrambled video signal by modulation of the horizontal sync. pulses of the scrambled video signal. An unscrambler derives the information from the horizontal sync. pulses, which it regenerates, and decodes the information and uses it to generate a vertical interval of correct timing to replace the dummy lines of the scrambled video signal, thereby producing an unscrambled video signal reproducible on a conventional TV receiver. The scrambling is further enhanced by varying the number of dummy lines which are used to replace different vertical intervals, thereby producing a video signal of variable field length, which is not susceptible of recording.