Jamming signal scrambling and descrambling systems for CATV

• US 4,748,667 A
• Filed: 11/04/1986
• Issued: 05/31/1988
• Est. Priority Date: 11/04/1986
• Status: Expired due to Term

• Current Assignee: Scientific-Atlanta Incorporated (Cisco Systems, Inc.)
• Original Assignee: Scientific-Atlanta (Cisco Systems, Inc.)
• Inventors: Lewis, Christopher P., LaFay, William P., Mobley, Joseph G. II, Farmer, James O., West, Lamar E. Jr., Montreuil, Leo, Kruse, Herman A., Thompson, Leo J., Little, Frank R. Jr., Kozushin, Anatoly
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US06/926,749
• Time in Patent Office: 574 Days
• Field of Search: 455/1, 455/286, 455/339, 380/7, 333/176, 333/155, 333/193
• US Class Current: 380/208
• CPC Class Codes: H04K 2203/14 for the transfer of light or images, e.g. for video-surveillance, for television or from a computer screen
• CPC Class Codes: H04K 3/42 characterized by the control of the jamming frequency or wavelength
• CPC Class Codes: H04K 3/43 characterized by the control of the jamming power, signal-to-noise ratio or geographic coverage area
• CPC Class Codes: H04K 3/825 by jamming
• CPC Class Codes: H04N 7/166 Passage/non-passage of the television signal, e.g. jamming, band suppression scrambling and descrambling H04N7/167

Abstract

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.

Claims

1. A system for processing television signals in the form of one sideband and the vestigial sideband of a picture carrier modulated by video and synchronization signals, including horizontal sync signals, in order to provide for the intelligible reception thereof by the TV receivers of certain subscribers, said system comprising means for combining said television signals with jamming signal energy the frequency of which is substantially at the frequency of one of the nulls in the spectrum of the modulation of said picture carrier by said horizontal sync signals means for transmitting said combined jamming and television signals to receiver locations, and means at said locations disposed ahead of said TV receivers defining a passband for the transmitted signals without substantial attenuation except at a notch essentially in the frequency region containing said jamming signal energy.

2. The system according to claim 1 wherein said jamming signal energy frequency is in the frequency region of said vestigial sideband.

3. The system according to claim 2 wherein said jamming signal energy is at the one of said nulls closest to said picture carrier.

4. The system according to claim 1 wherein said jamming signal energy is centered approximately at at least one of following frequencies which respectively are offset in KHz from the frequency of the picture carrier by ±

196.7, ±

228.1, ±

401.2, ±

448.4, ±

621.5, ±

653.0, ±

826.0, ±

873.3, ±

1046.3, and ±

1077.8.

5. The system according to claim 1 wherein said jamming signal energy frequency is also approximately at odd integral multiples of the frequency of one-half the repetition frequency of said horizontal sync signals.

6. The system according to claim 1 wherein said jamming signal energy frequency is also offset from the picture carrier frequency by a frequency which approximately is in a range ±

5 KHz about an integral multiple of 25 KHz.

7. The system according to claim 1 wherein said jamming signal energy frequency also is approximately at odd integral multiples of one-half the repetition frequency of said horizontal sync signals and is also offset from the picture carrier frequency in a range ±

5 KHz about integral multiples of 25 KHz.

8. The system according to claim 2 further comprising preemphasis means for increasing the amplitude of said transmitted television signals in said one sideband and offset from said picture carrier frequency by the same offset as said jamming signal energy has from said picture carrier whereby to compensate for the removal of said energy by said notch attenuation means.

9. The system according to claim 2 further comprising means in said transmitting means for reducing the amplitude of said television signal'"'"'s vestigial sideband to an extent sufficient to reduce artifacts arising from the removal of the jamming signal energy by said notch attenuation means.

10. The system according to claim 1 further comprising means for modulating said jamming signal with another signal at the frequency of said horizontal sync and offset in phase so that the envelope of said modulated jamming signal is reduced in amplitude when the sync signals of said television signal are present, said combining means being operative to combine said modulated jamming signal with said television signals.

11. The system according to claim 10 wherein said jamming signal modulating means includes means operative to suppress said jamming signal and provide signals corresponding to the modulation sidebands of said jamming signal and said another signal as said modulated jamming signal.

12. The system according to claim 10 further comprising means for inhibiting said jamming signal modulating means during the vertical synchronizing interval of said television signals.

13. The system according to claim 1 further comprising means for generating said television signals at intermediate frequency, jamming signal generating means operative at intermediate frequency, said combining means also being operative at intermediate frequency, and said transmitting means including up-converter means for translating said combined television and jamming signals to a predetermined radio frequency channel for transmission.

14. The system according to claim 1 further comprising means for generating said television signals at intermediate frequency, means for up converting said television signals to a predetermined radio frequency channel, means for generating said jamming signal at radio frequency in said channel, said combining means being operative to combine said up-converted television signals with said jamming signal for transmission in said channel.

15. The system according to claim 1 further comprising jamming signal generating means including means for providing, with said jamming signal and picture carrier, a first signal of frequency equal to the difference between the picture carrier frequency and the jamming signal frequency which is of a frequency which is an integral multiple of a second signal of frequency related to the horizontal sync frequency, and means responsive to said first and second signals and means for phase locking said jamming signal at a frequency which is offset from said picture carrier frequency by a said multiple of said second signal frequency.

16. The system according to claim 15 further comprising means operative to provide said jamming signal offset at a frequency which is about one-half between integral multiples of said horizontal sync frequency.

17. The system according to claim 16 wherein said means defined in claim 16 is provided by means responsive to said horizontal sync signal for generating said second signal at a frequency equal to an integral multiple of one-half the horizontal sync frequency.

18. The system according to claim 16 wherein said second signal is of the horizontal sync frequency, and the means defined in claim 16 comprises means for modulating said jamming signal with a signal equal to an odd multiple of the horizontal sync frequency, and suppressing said jamming signal frequency to produce as said jamming signal a pair of sideband signals, one at said jamming frequency plus said odd submultiple frequency and the other at said jamming signal frequency minus said odd submultiple frequency.

19. The system according to claim 1 further comprising means for offsetting the frequency of said jamming signal by a certain frequency offset, temperature responsive means for enabling said offsetting means only when the temperature has changed from a nominal temperature by a certain amount to compensate for the effect of temperature upon said attenuating means.

20. The system according to claim 1 wherein said means at said locations includes means defining an all-pass network between an input for said combined television and jamming signals and an output for said television signals, and in addition to said all-pass network at least one surface acoustic wave (SAW) device resonant at the frequency of said notch between said input and said output.

21. The system according to claim 20 wherein said all-pass network is defined by capacitors connected between said input and said output and having a function therebetween, a resistor connected in shunt with said input to said junction, to define a "T" circuit, said SAW device being connected across said capacitors in bridging relationship with said "T" circuit.

22. The system according to claim 20 wherein said all-pass network includes a first branch and a second branch both resonant at said notch frequency, said first branch being in series relationship with said input and output, said second branch being in shunt relationship between said input and output, and the Q'"'"'s of said first and second branches being approximately equal.

23. The system according to claim 22 wherein said first and second branches are parallel resonant circuits.

24. The system according to claim 22 wherein said first branch is a parallel resonant circuit and said second branch is a series resonant circuit.

25. The system according to claim 24 wherein said second branch has first and second capacitors connected between said input and output and having a junction therebetween, and an inductor and resistor connected to said junction in shunt relationship with said first and second capacitors.

26. The system according to claim 22 wherein said first circuit includes inductive and capacitive elements defining a passband phase characteristic with a notch at said jamming signal frequency and connected to said SAW device by first and second inductors, one of which is connected to said input and the other to said output, said second circuit including third and fourth inductors respectively connected to opposite ends of said SAW device in shunt relationship with said input and output to define a passband characteristic with a notch at said jamming signal frequency.

27. The system according to claim 20 further comprising a SAW device having a dual SAW resonator connected between said input and output by first and second transformers having primary and secondary windings connected in shunt relationship with said input and output, a series resonant circuit connected between said input and output, and a parallel resonant circuit connected across said dual SAW resonator device.

28. The system according to claim 22 further comprising a second SAW device resonant at said notch frequency and connected in said second circuit in shunt relationship with said input and output.

29. The system according to claim 28 wherein said second circuit has first and second inductors connected between said input and said output and having a junction therebetween, said second SAW device being connected to said junction at one end thereof.

30. The system according to claim 22 branches wherein a plurality of said all-pass circuits as defined in claim 22 and connected in cascade between said input and output with the SAW devices thereof connected in series with each other between said input and said output.

54. The system according to claim 46 branches wherein a plurality of said all-pass circuits as defined in claim 22 are connected in cascade between said input and output with the SAW devices thereof connected in series with each other between said input and said output.

65. The network according to claim 55 branches wherein a plurality of said all-pass circuits as defined in claim 22 and connected in cascade between said input and output with the SAW devices thereof connected in series with each other between said input and said output.

31. A system for processing television signals in order to provide for the intelligible reception thereof by the TV receivers of certain subscribers, in the form of one full sideband and the vestigial sideband of a picture carrier modulated by video and synchronization signals, including horizontal sync pulses, which also imposes a spectrum centered about the frequency of said picture carrier, said spectrum consisting of components at harmonics of the frequency of said horizontal sync pulses having nulls at the frequencies which are equal to the reciprocal of the duration of said horizontal sync pulses, said system comprising means for combining said television signals with jamming signal energy the frequency of which is offset from said picture carrier and is within one of said nulls within the range where the amplitude of said spectrum is within about 1% of the level of said picture carrier, means for transmitting said combined television and jamming signals to TV receiver locations, and means at said locations disposed ahead of said receivers defining a passband for the transmitter signals without substantial attenuation except at a notch at the frequency of said jamming signal energy.

32. The system according to claim 31 wherein said jamming frequency energy is also approximately at one of the nulls of said spectrum closest to said picture carrier.

33. The system according to claim 32 wherein said jamming signal energy is also between the frequencies of two of said harmonic components.

34. The system according to claim 33 wherein said jamming signal energy is also within ±

5 KHz of a multiple of 25 KHz offset from the frequency of said picture carrier.

35. The system according to claim 34 wherein said jamming signal energy is approximately at a frequency selected from the group consisting of the following frequencies which are frequencies in KHz offset above and below the picture carrier frequency of 196.7, 228.1, 401.2, 448.4, 621.5, 653.0, 826.0, 873.3, 1046.1, and 1077.8.

36. The system according to claim 31 wherein said jamming signal energy is in the vestigial sideband.

37. The system according to claim 36 further comprising preemphasis means for increasing the amplitude of said transmitted television signals in said one sideband and offset from said picture carrier frequency by the same offset as said jamming signal energy has from said picture carrier whereby to compensate for the removal of said energy by said notch attenuation means.

38. The system according to claim 36 further comprising means in said transmitting means for reducing the amplitude of said television signal'"'"'s vestigial sideband to an extent sufficient to reduce artifacts arising from the removal of the jamming signal energy by said notch attenuation means.

39. The system according to claim 31 further comprising means for modulating said jamming signal with another signal at the frequency of said horizontal sync and offset in phase so that the envelope of said modulated jamming signal is reduced in amplitude when the sync signals of said television signal are present, said combining means being operative to combine said modulated jamming signal with said television signals.

40. The system according to claim 39 wherein said jamming signal modulating means includes means operative to suppress said jamming signal and provide signals corresponding to the modulation sidebands of said jamming signal and said another signal as said modulated jamming signal.

41. The system according to claim 40 further comprising means for inhibiting said jamming signal modulating means during the vertical synchronizing interval of said television signals.

42. The system according to claim 31 further comprising means for generating said television signals at intermediate frequency, jamming signal generating means operative at intermediate frequency, said combining means also being operative at intermediate frequency, and said transmitting means including up-converter means for translating said combined television and jamming signals to a predetermined radio frequency channel for transmission.

43. The system according to claim 31 further comprising means for generating said television signals at intermediate frequency, means for up converting said television signals to a predetermined radio frequency channel, means for generating said jamming signal at radio frequency in said channel, said combining means being operative to combine said up-converted television signals with said jamming signal for transmission in said channel.

44. The system according to claim 31 further comprising means for offsetting the frequency of said jamming signal by a certain frequency offset, temperature responsive means for enabling said offsetting means only when the temperature has changed from a nominal temperature by a certain amount to compensate for the effect of temperature upon said attenuating means.

45. The system according to claim 31 wherein said means at said locations includes means defining an all-pass network between an input for said combined television and jamming signals and an output for said television signals, and in addition to said all-pass network at least one surface acoustic wave (SAW) device resonant at the frequency of said notch between said input and said output.

46. The system according to claim 45 wherein said all-pass network includes a first branch and a second branch both resonant at said notch frequency, said first branch being in series relationship with said input and output, said second branch being in shunt relationship between said input and output, and the Q'"'"'s of said first and second branches being approximately equal.

47. The system according to claim 46 wherein said first and second branches are parallel resonant circuits.

48. The system according to claim 46 wherein said first branch is a parallel resonant circuit and said second branch is a series resonant circuit.

49. The system according to claim 48 wherein said second branch has first and second capacitors connected between said input and output and having a junction therebetween, and an inductor and resistor connected to said junction in shunt relationship with said first and second capacitors.

50. The system according to claim 46 wherein said first circuit includes inductive and capacitive elements defining a passband phase characteristic with a notch at said jamming signal frequency and connected to said SAW device by first and second inductors one of which is connected to said input and the other to said output, said second circuit including third and fourth inductors respectively connected to opposite ends of said SAW device in shunt relationship with said input and output to define a passband characteristic with a notch at said jamming signal frequency.

51. The system according to claim 45 further comprising a SAW device having a dual SAW resonator connected between said input and output by first and second transformers having primary and secondary windings connected in shunt relationship with said input and output, a series resonant circuit connected between said input and output, and a parallel resonant circuit connected across said dual SAW resonator device.

52. The system according to claim 46 further comprising a second SAW device resonant at said notch frequency and connected in said second circuit in shunt relationship with said input and output.

53. The system according to claim 52 wherein said second circuit has first and second inductors connected between said input and said output and having a junction therebetween, said second SAW device being connected to said junction at one end thereof.

55. A network for removing a jamming signal combined with a television signal, said jamming signal being located in the vestigial sideband of said television signal or in the full sideband within a frequency range from the picture carrier including the spectrum of the modulation of said picture carrier by the horizontal sync signals of said television signal of amplitude of significant relationship to the amplitude of said picture carrier, said network comprising means defining a passband for said combined television and jamming signal without substantial attentuation except at a notch containing the frequency of said jamming signal, and where said last named means includes means defining an all-pass network between an input for said combined television and jamming signals and an output for said television signals and in addition to said all-pass network at least one surface acoustic wave (SAW) device resonant at the frequency of said notch between said input and said output.

56. The network according to claim 55 wherein said all-pass network is defined by capacitors connected between said input and said output and having a junction therebetween, a resistor connected in shunt with said input to said junction to define a "T" circuit, said SAW device being connected across said capacitors in bridging relationship with said "T" circuit.

57. The network according to claim 55 wherein said all-pass network includes a first branch and a second branch both resonant at said notch frequency, said first branch being in series relationship with said input and output, said second branch being in shunt relationship between said input and output, and the Q'"'"'s of said first and second branches being approximately equal.

58. The network according to claim 57 wherein said first and second branches are parallel resonant circuits.

59. The network according to claim 57 wherein said first branch is a parallel resonant circuit and said second branch is a series resonant circuit.

60. The network according to claim 59 wherein said second branch has first and second capacitors connected between said input and output and having a junction therebetween, and an inductor and resistor connected to said junction in shunt relationship with said first and second capacitors.

61. The network according to claim 57 wherein said first circuit includes inductive and capacitive elements defining a passband phase characteristic with a notch at said jamming signal frequency and connected to said SAW device by first and second inductors one of which is connected to said input and the other to said output, said second circuit including third and fourth inductors respectively connected to opposite ends of said SAW device in shunt relationship with said input and output to define a passband characteristic with a notch at said jamming signal frequency.

62. The network according to claim 55 further comprising a SAW device having a dual SAW resonator connected between said input and output by first and second transformers having primary and secondary windings connected in shunt relationship with said input and output, a series resonant circuit connected between said input and output, and a parallel resonant circuit connected across said dual SAW resonator device.

63. The network according to claim 57 further comprising a second SAW device resonant at said notch frequency and connected in said second circuit in shunt relationship with said input and output.

64. The network according to claim 63 wherein said second circuit has first and second inductors connected between said input and said output and having a junction therebetween, said second SAW device being connected to said junction at one end thereof.