There is disclosed a wired television system comprising a source of television signals supplying signals to a transmission network, subscriber stations connected to the network, means for preventing reception of transmitted signals by at least one subscriber station, and means for overriding the preventing means to enable that subscriber to receive the transmitted signals. The television signals are heterodyned with a scrambling signal to provide the transmitted signals, and the scrambling signal is transmitted over the network. At the subscriber station, the transmitted signals and the scrambling signal are heterodyned to recover the television signal.
An interface for subscription television reception which restores the program selection function to the tuner of the television receiver. This is of particular importance to subscribers using remote control receivers. Subscription television signals are split into two substantially identical components, one of which is fed to the tuner of the television receiver and the other of which is passed through a band reject filter to an adder. The intermediate frequency output of the tuner is converted to a predetermined carrier frequency in the television broadcast band and, as so converted, fed to the other input of the adder. The output of the adder is, in turn, fed to a conventional subscription television converter/decoder, which is set to select the program on the predetermined carrier frequency and decode the same. The converter/decoder output is converted to the intermediate frequency carrier for amplification and further processing in the intermediate frequency circuitry of the television receiver.
In order to control subscriber access to selected television programs in a CATV system, nonstandard horizontal synchronizing pulses, having a greater amplitude and either a higher or lower pulse repetition rate than the contained horizontal synchronizing pulses, are selectively added to those television programs to be controlled. As a result, the television receiver of a nonpaying subscriber interprets the nonstandard pulses as being valid horizontal synchronizing pulses thereby preventing the receiver from synchronizing its line scanning with that of the television program rendering the picture produced therefrom unviewable.
Television signal scrambling is effected by combining moderate level trap-attenuation of the visual carrier frequency with an injected fm-modulated interfering signal to effect, by adjustment of amplitude and fm-modulation levels, satisfactory picture scrambling and overpowering audio distortion in the user's television receiver.
Scrambling and descrambling systems utilizing jamming signals provide improved pictures with minimal distortion due to ghosts and artifacts. The television signal is combined with a jamming signal or signals located preferably in the vestigial sideband (VSB) of the modulated picture carrier and at about a null in the spectrum of the modulation of the picture carrier by the horizontal sync. The jamming signal or signals also preferably are placed between the harmonic components of the horizontal sync which define the horizontal sync spectrum and at frequencies which comply with governmental regulations respecting frequency locations of strong signals of CATV purposes. The jamming signals are generated by phase locking to the horizontal sync signals of the television signals or to a submultiple of the horizontal sync frequency. Artifacts are further reduced by preemphasis of the transmitted television signal in the sideband opposite to that in which the jamming signal or signals are located and spaced by an equal frequency increment from the location of the jamming signal energy. In order to extract the jamming signal, so as to descramble the television signal for reproduction in the subscriber's television receiver, a network including at least one surface acoustic wave (SAW) resonator device is embedded in an all-pass network which allows essentially lossless transmission of the television signal spectrum, except for the jamming signal energy and enables that energy to be located close to (e.g., approximately 228 KHz) from the picture carrier in the VSB for enhanced security.
A plurality of video lines in a raster scan video image are scrambled by delaying a first video line in time equal to the horizontal line scan time for the raster scan video field to produce a delayed first video line. The delayed first video line is inverted to produce an inverted delayed first video line and one of the delayed first video line, the inverted delayed first video line and a null signal is added to a second horizontal video line to produce a horizontal line of a scrambled video signal. The scrambled horizontal lines of video information are descrambled by delaying a first scrambled horizontal video line in time equal to the horizontal line scan time for the raster scan video field to produce a delayed first scrambled video line. The delayed first scrambled video line is inverted to produce an inverted delayed first scrambled video line and one of the delayed first scrambled video line, the inverted delayed first scrambled video line and a null signal is added to a second scrambled horizontal video line and to a feedback signal to produce a descrambled horizontal video line.
