______________________________________                                    Frequency                                                                 (from center)  Attenuation                                                ______________________________________                                      0 MHZ        -38.7 dB                                                   -2.25 MHz      -7.5 dB                                                    -1.5 MHz       -22.5 dB                                                   +1.33 MHz      -26.7 dB                                                   -6.0 MHz        0.0 dB                                                    +6.0 MHz        0.0 dB                                                    ______________________________________

The approximate location of the video carrier is shown at 14, and the approximate location of the audio carrier is shown at 16. The maximum attenuation is 38.7 dB, and this is located at the frequency of the carrier plus 2.25 MHz.

With reference to FIG. 3, the distortion curve is shown at 18, and a typical distorted television signal is shown at 20. The video carrier is shown at 22, and the audio carrier is shown at 24.

FIG. 4 shows a comparison between a typicaldistorted television signal 26 and a restoredsignal 28 during the picture transmission part of the signal.

Referring again to FIG. 1, the gated jamming pulses of the invention will be described. The distortion-restoration system described with reference to FIGS. 2 through 4 provides adequate jamming of television signals for a large majority of the television receivers in use today. Some newer receivers, however, may be capable of producing a "viewable" picture from the distorted signal as shown bycurve 26 of FIG. 4. Accordingly, applicants additionally provide two jamming signals between the audio and video carriers, the jamming signals having amplitudes such that they are each equal to the video carrier amplitude resulting at 50. These jamming signals are supplied only during the vertical and horizontal blanking periods, and the combination of the distortion and the gated jamming signals provides complete jamming for even state of the art receivers.

The gated jamming signals are provided by afirst oscillator 30, which produces a signal spaced from the video carrier by about 1.4 MHz, and asecond oscillator 32, which produces a signal spaced from the video carrier by about 2.258 MHz.

The video signal from the video source is supplied to avideo loop 36, and the loop passes through async separator 38. The sync separator provides a series of pulses in accordance with the horizontal sync pulses, and the vertical sync pulses are derived from these. Acomposite blanking generator 40 generates avertical signal 42 which controls a mixer 44 and ahorizontal signal 46 which controls amixer 48. The mixers are essentially gates controlled by the horizontal and vertical signals to allow the introduction of the signals from the

oscillators

30 and 32 to a hybrid combiner 34 only during respective horizontal and vertical blanking intervals. The hybrid combiners themselves are known and provide low loss coupling of the signals from the input ports to the common output port.

The video signal which has been modulated by an intermediate frequency and which is supplied at 4 is combined with the gated jamming signals, and this combination is subjected to the buffer and

distortion amplifiers

8, 10, and 12 as described above. The resulting signal at 50 is returned to the modulator for combination with the audio signal and transmission to the cable system.

While the gated jamming signals have been described as comprising carrier signals, they alternatively comprise noise. In a practical embodiment, the bandwidth of the noise was 3 MHz, but this may be larger or smaller. In accordance with this embodiment, the

oscillators

30 and 32 are replaced by a noise generator which produces a noise signal for combination with the video signal in lieu of the jamming signals at single frequencies.

The gated jamming signals are inherently removed in large measure by therestoration filter 15 having the characteristics illustrated in FIG. 2. The restoration filter reduces the amplitude of the center of the signal between the audio and video carriers by about 30 dB with respect to the video carrier. Thus, the jamming signals are reduced in amplitude by about 97%. The residual 3% has been found to be small enough to permit the television receiver to read the information it is required to find in the blanking intervals, such as the horizontal sync signal, the color burst signal, and vertical interval signals. This remaining 3% can, however, reduce the quality of the picture if it is present during the interval when the signal carries picture information. Because these jamming signals are gated, however, they are not present when the picture information is transmitted and do not interfere with the production of a high quality picture by the receiver.

It will be appreciated that a unique technique for improving the quality of a television picture and for preventing unauthorized of television signals has been described. Modifications within the scope of the appended claims will be apparent to those of skill in the art.