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Title: Scrambler and decoder for a television signal
Claims: What is claimed is 1. In a system for scrambling and decoding a television signal modulated on a normal carrier which is replaced with a scrambling carrier having the same frequency as the normal carrier but with a predetermined phase difference therefrom and where the scrambled television signal is decoded at a receiving end by regenerating the normal carrier from the scrambling carrier for the latter's replacement by the regenerated normal carrier the improvement comprising means for generating a coding signal of a frequency selected to enable modulation of the scrambling carrier for enhanced security; means responsive to the coding signal for amplitude modulating of the scrambling carrier; means responsive to the coding signal for frequency modulating of the scrambling carrier; means at the receiving end for detecting the frequency modulation to reproduce the coding signal; and means for replacing the scrambling carrier at the receiving end with the inverse amplitude modulated normal carrier to provide a normally displayable television signal. 2. The improved television scrambling and decoding system as claimed in claim 1 wherein the coding signal is a signal selected of sufficiently low frequency to inhibit production of non-removable and objectional interference with the television signal. 3. The improved television scrambling and decoding system as claimed in claim 2 and further including a frequency variable oscillator of an intermediate frequency (IF); means responsive to the IF oscillator for producing video and audio modulated IF signals, and wherein said coding signal is applied to both the frequency variable oscillator and said amplitude modulating means to simultaneously generate amplitude and frequency modulation of the scrambling carrier. 4. The improved television scrambling and decoding system as claimed in claim 3 wherein the frequency modulation detecting means further includes means including a receiver IF oscillator operating at a receiver IF for phase locking the received television signal to the receiver oscillator. 5. The improved television scrambling and decoding system as claimed in claim 4 wherein the phase locking means further includes means including a variable receiver local oscillator for converting the received scrambled television signal to the receiver IF; and a phase detector responsive to the receiver IF oscillator and the receiver IF from the converting means to produce an output signal representative of the difference in phase therebetween, said signal being applied to the variable receiver local oscillator with a magnitude and polarity selected to establish phase lock between the receiver IF and the receiver IF oscillator, said signal also being representative of the coding signal. 6. The improved television scrambling and decoding system as claimed in claim 5 wherein the normal carrier generating means further includes means responsive to the receiver IF oscillator for producing a phase shift carrier whose phase is substantially the phase of the normal carrier; means for generating the inverse of the coding signal; and a modulator coupled to the inverse coding signal and the normal carrier output from the phase shifting means for modulation thereof by the coding signal. 7. An apparatus for scrambling an input television signal amplitude modulated on a normal carrier comprising means for producing a scrambling carrier signal of the same frequency as the normal carrier signal and with a preselected phase difference therebetween; means for generating a coding signal of a frequency selected to enable modulation of the scrambling carrier for enhanced security; means for amplitude modulating the scrambling carrier with the coding signal; and means for frequency modulating the normal and scrambling carrier signals to impose a pilot signal representative of the coding signal; and means for substantially replacing said normal carrier in the carrier modulated television signal with the amplitude modulated scrambling carrier. 8. The apparatus for scrambling an input television signal as claimed in claim 7 wherein the frequency modulating means further includes a variable local oscillator operating at the carrier frequency, said coding signal being coupled to the variable oscillator to produce frequency variation thereof in correspondence with the coding signal; and means for applying the output of the local oscillator to generate a common frequency source for said normal and scrambling carriers. 9. The apparatus for scrambling an input television signal as claimed in claim 8 wherein the coding signal generating means produces a coding signal characterized with information for use at a receiving location. 10. The apparatus for scrambling an input television signal as claimed in claim 9 wherein the coding signal generating means further produces a coding signal whose frequency is selected sufficiently low to inhibit production of non-removable and objectionable interference of the television signal at a receiving end. 11. An apparatus for decoding a received scrambled television signal applied with a scrambling input carrier which is out of phase with a normal unscrambled carrier and amplitude modulated for enhanced security comprising means for producing an oscillator signal representative of a desired intermediate frequency (IF) of the scrambling carrier; means responsive to the received television signal for phase locking an IF converted representation of the received scrambled television signal to the oscillator signal; means coupled to the phase locking means for producing a coding signal representative of a frequency modulation in the scrambling carrier; means responsive to the oscillator signal for generating a normal carrier signal; means for amplitude modulating the normal carrier signal with the inverse of the coding signal; and means for combining the amplitude modulated normal carrier with the phase locked IF scrambling carrier signal to remove the amplitude modulation therefrom for regeneration of an unscrambled television signal. 12. The apparatus for decoding a received scrambled television signal as claimed in claim 11 wherein the normal carrier signal modulating means further includes means for inverting the coding signal; and an amplitude modulator coupled to the normal carrier signal and the inverted coding signal for amplitude modulation of the normal carrier. 13. The apparatus for decoding a received scrambled television signal as claimed in claim 12 wherein the combining means further includes an attenuator responsive to the amplitude modulated normal carrier for amplitude adjustment thereof to a level selected to cancel the scrambled carrier and its amplitude modulation. 14. The apparatus for decoding a received scrambled television signal as claimed in claim 11 and further including switching means operatively located to interrupt the coupling of the normal carrier to the combining means for control over access to the received scrambled television signal; and means responsive to the coding signal for generating a control signal to said switching means to determine access to the received scrambled television signal. 15. The apparatus for decoding a received scrambled television signal as claimed in claim 11 wherein the phase locking means further includes means including a variable local oscillator for converting the received television signal to an IF frequency for viewing on a television receiver; a phase detector responsive to the oscillator signal and the compatible IF frequency for producing an output signal having a polarity and magnitude indicative of the phase difference therebetween, said output signal being coupled to the variable local oscillator for frequency control thereof in a direction selected to establish phase lock between the compatible IF frequency and the oscillator signal. 16. A method for scrambling a television signal which is decoded at the receiving end to which the television signal is sent in a scrambled form comprising the steps of producing a coding signal selected to enable enhanced security scrambling of the television signal; frequency modulating a normal carrier with the coding signal; amplitude modulating the frequency modulated normal carrier with a television signal; phase shifting the frequency modulated normal carrier to generate a scrambling carrier which is of the same frequency as the normal carrier but with a predetermined scrambling phase difference therebetween; amplitude modulating the scrambling carrier with the coding signal; and replacing the normal carrier in the television signal modulated normal carrier with the amplitude modulated carrier for enhanced security television signal. 17. The method for scrambling a television signal as claimed in claim 16 wherein the coding signal producing step is characterized by the generation of a coding signal formed to convey information. 18. The method for scrambling a television signal as claimed in claim 17 wherein the coding signal is of a low frequency selected to prevent the generation of non-removable interference with the television signal at the receiving end. 19. The method for scrambling a television signal as claimed in claim 16 and further including a method for decoding the scrambled television signal at the receiving end comprising the steps of removing the frequency modulation of the scrambling carrier; regenerating the coding signal from the received scrambled television signal; regenerating a normal carrier from the scrambling carrier; amplitude modulating the regenerated normal carrier with the inverse of the regenerated coding signal; and replacing the scrambling carrier with the inverse modulated regenerated normal carrier to reproduce a normal carrier amplitude modulated television signal for display by a television receiver. 20. The method for scrambling and decoding a television signal as claimed in claim 19 wherein the coding signal regeneration and frequency modulation steps further include the steps of generating a fixed intermediate frequency (IF) oscillator signal; converting the received scrambled television signal to an IF television signal frequency with a variable local oscillator; phase locking the IF television signal frequency to the IF oscillator signal by controlling the frequency and phase of the variable oscillator with a phase detector output signal indicative of phase lock, whereby the IF oscillator signal is representative of the scrambling carrier without frequency modulation and the output signal represents the regenerated coding signal. Other info: Inventors: Aaronson, Gerald (Brookline, MA, US) Murphy, William D. (Burlington, MA, US) Application Number: 494653 Filing Date: 1974-08-05 Publication_date: 1976-02-03 Assignee: GTE Laboratories Incorporated (Waltham, MA) Primary Class(es): 380/219 380/235, 380/240, 455/109 Other Classes: US Patent Ref:
Other Refs: Primary Examiner: Farley, Richard A. Assistant Examiner: Buczinski, S. C. Attorney: Kriegsman; Irving M, Hart; Leslie J. |
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