US3852519A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Video and audio encoding/decoding system employing suppressed carrier modulation
Assignee: Optical Systems Corp
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Filing: 1972-10-20
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Granted: 1974-12-03
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Expires: 1992-10-20
Abstract
Abstract In a television transmission system, particularly a community antenna television system (CATV), although also applicable to broadcast television transmission, a system is disclosed for encoding both the video and audio components of a channel thus rendering the transmitted channel secure against unauthorized viewing and listening, by full or partial suppression of the video carrier such that the video modulation becomes inverted and the minimum 12.5% video carrier level required for intercarrier demodulation of the audio is lost. Sufficient information is transmitted within the encoded channel to permit a decoder at the receiver to produce a signal at the frequency of the suppressed video carrier, and of proper phase and amplitude, to restore the video carrier upon adding it to the suppressed video carrier.
Inventors
- 👤 P Court
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-27 07:55
CPC Classifications
H; H04; H04N; H04N7/00; H04N7/16; H04N7/167; H04N7/171
Claims Analysis
Total Claims: 35
Claim 1
Independent Claim
239 words
In a television communication system, a method of encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized television receiver, and for maintaining said television program signal recoverable by an authorized receiver, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said modulated video carrier being combined with a frequency modulated audio carrier, said method being comprised of suppressing said modulated video carrier of said television program signal by a factor sufficient for at least portions of said modulated video carrier to be reduced below normal peak levEl at least part of the time, thus producing a suppressed video carrier whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, wherein suppression of said modulated video carrier is sufficient during at least portions thereof to prevent satisfactory intercarrier demodulation of said frequency modulated audio carrier by an unauthorized receiver, whereby intelligible reception of the audio portion of said television program signal is prevented, and wherein suppression of said modulated vido carrier is to such an extent that proper line synchronization of an unauthorized receiver fails sufficiently for display of an intelligible picture to become impossible due to peak inverted video signals having an amplitude more than that of synchronizing pulses amplitude modulated on said video carrier.
Claim 2
Dependent Claim
239 words
In a television communication system, a method of encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized television receiver, and for maintaining said television program signal recoverable by an authorized receiver, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said modulated video carrier being combined with a frequency modulated audio carrier, said method being comprised of suppressing said modulated video carrier of said television program signal by a factor sufficient for at least portions of said modulated video carrier to be reduced below normal peak levEl at least part of the time, thus producing a suppressed video carrier whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, wherein suppression of said modulated video carrier is sufficient during at least portions thereof to prevent satisfactory intercarrier demodulation of said frequency modulated audio carrier by an unauthorized receiver, whereby intelligible reception of the audio portion of said television program signal is prevented, and wherein suppression of said modulated vido carrier is to such an extent that proper line synchronization of an unauthorized receiver fails sufficiently for display of an intelligible picture to become impossible due to peak inverted video signals having an amplitude more than that of synchronizing pulses amplitude modulated on said video carrier.
Claim 3
Dependent Claim
49 words
The method as defined in claim 1 wherein suppression of said modulated video carrier is to such an extent that said synchronizing pulses have an amplitude insufficient to be detected by an unauthorized television receiver, whereby totally false and time-varying synchronizing information is derived from said modulated video carrier.
Claim 4
Dependent Claim
162 words
In a television communication system, a method a defined in claim 1 wherein information for use in restoring said moulated video carrier to its normal peak level in an authorized receiver is transmitted in the form of the interdependence in phase and frequency between a reference subcarrier and reference carrier, where said reference subcarrier is transmitted on a carrier and where said reference carrier is derived from said reference subcarrier and said video carrier as the frequency difference between said video carrier and the product of said reference subcarrier multiplied by a constant for a predetermined intercarrier frequency difference between said video carrier and said reference carrier to enable an authorized receiver to generate a local signal of proper frequency, phase and amplitude from the direct relationship, through multiplication, between the reference subcarrier frequency and the intercarrier difference frequency, said local signal to be added to said modulated video carrier received for restoration of the normal level of said modulated video carrier.
Claim 5
Dependent Claim
117 words
A method as defined in claim 3 wherein said authorized receiver restores said modulated video carrier to its normal peak level before normal receiver processing by continuously detecting said subcarrier reference, multiplying said detected subcarrier reference signal by said constant to produce a local product signal at the frequency of said intercarrier frequency, and effectively adding said local product signal to said reference carrier of said television program signal to produce a signal of the same frequency and phase as said video carrier of said television program signal for synchronizing a local signal generator in frequency and phase, and adding said local signal to said television program signal with just sufficient to restore said modulated video carrier.
Claim 6
Dependent Claim
25 words
A method as defined by claim 4 wherein said reference subcarrier is transmitted on a carrier within the same television channel as said video carrier.
Claim 7
Dependent Claim
31 words
A method as defined by claim 5 wherein said audio carrier is employed as the carrier for said reference subcarrier, and said reference subcarrier is amplitude modulated on said audio carrier.
Claim 8
Dependent Claim
128 words
A method as defined in claim 1 wherein suppression of said modulated video carrier is by a factor of 75% normal peak value, and wherein information for use in restoring said modulated video carrier in an authorized receiver is transmitted in the form of keying pulses synchronized with horizontal sync pulses in said modulated video carrier to enable an authorized receiver to detect said keying pulses and, in response thereto, gate bursts of modulated video carrier during horizontal sync periods to a local signal generator to synchronize said local signal generator in frequency and phase with said modulated vIdeo carrier received, whereby the output of said local signal generator may be added to said television program signal for restoration of said modulation video carrier at said authorized receiver.
Claim 9
Dependent Claim
22 words
A method as defined by claim 7 wherein said keying pulses are modulated on a carrier for transmission to said authorized receiver.
Claim 10
Dependent Claim
22 words
A method as defined by claim 8 wherein sid keying-pulse carrier is within the same television channel as said modulated video carrier.
Claim 11
Dependent Claim
26 words
A method as defined by claim 9 wherein said keying-pulse carrier is said audio carrier, and said keying pulses are amplitude modulated on said audio carrier.
Claim 12
Dependent Claim
187 words
The method of claim 3 wherein said information for use ijn restoring the suppressed video carrier in an authorized receiver is comprised of a reference subcarrier signal of substantially constant frequency and an unmodulated reference carrier derived from said reference subcarrier signal by multiplying said reference subcarrier signal by a fixed multiplier and mixing the product with unmodulated video carrier from said video carrier generator, and wherein said frequency modulated audio carrier is amplitude modulated by said reference subcarrier signal, the frequency of said reference subcarrier signal being selected to be sufficiently low so that modulation sidebands do not extend beyond the upper and lower band ends, whereby variations in the phase and frequency of said reference carrier with respect to said modulated video carrier due to any variation in phase of said reference subcarrier signal are present also in said modulated audio carrier, but scaled down by a factor equal to the multiplier used for deriving said reference carrier, thereby conveying a precise phase reference of said modulated video carrier for use in an authorized receiver for restoring said modulated video carrier to normal peak level.
Claim 13
Dependent Claim
63 words
The method of claim 11 wherein an authorized receiver decodes an encoded transmission by generating an unmodulated signal of predetermined amplitude at the frequency of said modulated video carrier in response to said reference subcarrier signal and said reference carrier, and adding said unmodulated signal to said encoded transmission being received, said predetermined amplitude being selected to just restore said modulated video carrier.
Claim 14
Dependent Claim
47 words
The method of claim 7 wherein said information for use in restoring the suppressed video carrier in an authorized receiver is comprised of keying pulses amplitude modulated on a carrier, said keying pulses being produced in response to detection of horizontal synchronizing pulses in the video signal.
Claim 15
Dependent Claim
59 words
The method of claim 13 wherein an authorized receiver produces a local signal synchronized in frequency and phase with said modulated video carrier by detecting keying pulses in said keying-pulse carrier and in response thereto gating a burst of suppressed video carrier cycles for use in synchronizing said local signal in frequency and phase with said modulated video carrier.
Claim 16
Dependent Claim
43 words
A method as defined in claim 1 wherein said factor is sufficient for amplitude modulation of the video intelligence of said modulated video carrier to become at least partially inverted in phase, thereby distorting the video intelligence envelope of said modulated video carrier.
Claim 17
Dependent Claim
212 words
In a television communication system, a method of encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized television receiver, and for maintaining said television program signal recoverable by an authorized receiver, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said modulated video carrier being combined with a frequency modulated audio carrier, said method being comprised of suppressing said modulated video carrier of said television program signal by a factor sufficient for at least portions of said modulated video carrier to be reduced below normal peak level at least part of the tIme, thus producing a suppressed video carrier whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, whereby suppression of said modulated video carrier is achieved by generating a carrier, phase inverting said carrier in a separate circuit from that used for amplitude modulation of said video carrier by a video signal to achieve said amplitude modulated video carrier, and adding a predetermined percentage of the inverted carrier to said amplitude modulated video carrier with the phase of said inverted video carrier adjusted to be 180* out of phase with said modulated video carrrier and the amplitude of said inverted video carrier.
Claim 18
Dependent Claim
212 words
In a television communication system, a method of encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized television receiver, and for maintaining said television program signal recoverable by an authorized receiver, said television program signal being comprised of a video carrier amplitude modulated by a video signal, said modulated video carrier being combined with a frequency modulated audio carrier, said method being comprised of suppressing said modulated video carrier of said television program signal by a factor sufficient for at least portions of said modulated video carrier to be reduced below normal peak level at least part of the tIme, thus producing a suppressed video carrier whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, whereby suppression of said modulated video carrier is achieved by generating a carrier, phase inverting said carrier in a separate circuit from that used for amplitude modulation of said video carrier by a video signal to achieve said amplitude modulated video carrier, and adding a predetermined percentage of the inverted carrier to said amplitude modulated video carrier with the phase of said inverted video carrier adjusted to be 180* out of phase with said modulated video carrrier and the amplitude of said inverted video carrier.
Claim 19
Dependent Claim
91 words
The method of claim 16 in a television transmission system employing a receiver which relys upon intercarrier demodulation between the modulated video carrier and the modulated audio carrier to develop an audio signal, wherein said percentage of modulated video carrier suppression is sufficient for the modulated video carrier to be less than 12.5% a significant period of time during each vertical synchronizing cycle, thereby periodically disturbing audio reception by an unauthorized receiver at a rate equal to the vertical synchronizing frequency to produce an audible buzz out of said unauthorized receiver.
Claim 20
Dependent Claim
15 words
The method of claim 17, wherein said percentage of modulated video carrier suppression is 75%.
Claim 21
Dependent Claim
183 words
In a television communication system, apparatus for encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized receiver, and for maintaining said television program signal recoverable by an unauthorized receiver, said television program signal being comprised of an amplitude modulated video carrier combined with a frequency modulated audio carrier, the combination comprising means for generating a video carrier signal of constant frequency and amplitude, means for amplitude modulating said video carrier signal by a video signal to produce said modulated video carrier, means for suppressing said modulated video carrier by a factor to produce a suppressed video carrier, said factor being sufficient for amplitude modulation of the video intelligence of said video carrier to be reduced below normal peak level at least part of the time, whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, and means for transmitting to all receivers of said system information for use by authorized receivers only to restore said modulated video carrier as received to a level it would have had if not suppressed before transmission.
Claim 22
Dependent Claim
183 words
In a television communication system, apparatus for encoding a transmission to prevent a television program signal from being intelligibly received by an unauthorized receiver, and for maintaining said television program signal recoverable by an unauthorized receiver, said television program signal being comprised of an amplitude modulated video carrier combined with a frequency modulated audio carrier, the combination comprising means for generating a video carrier signal of constant frequency and amplitude, means for amplitude modulating said video carrier signal by a video signal to produce said modulated video carrier, means for suppressing said modulated video carrier by a factor to produce a suppressed video carrier, said factor being sufficient for amplitude modulation of the video intelligence of said video carrier to be reduced below normal peak level at least part of the time, whereby intelligible reception of said television program signal by an unauthorized receiver is prevented, and means for transmitting to all receivers of said system information for use by authorized receivers only to restore said modulated video carrier as received to a level it would have had if not suppressed before transmission.
Claim 23
Dependent Claim
41 words
Apparatus as defined in claim 19 wherein said factor is sufficient for amplitude modulation of the video intelligence of said modulated video carrier to become at least partially inverted in phase, thereby distorting the video intelligence envelope of said modulated carrier.
Claim 24
Dependent Claim
62 words
Apparatus as defined in claim 19 wherein said factor is sufficient to suppress said modulated video carrier to an extent that proper line synchronization at an unauthorized receiver fails sufficiently for display of an intelligible picture to be impossible due to peak inverted video signal portions having an amplitude more than that of synchronizing pulses amplitude modulated on said video carrier signal.
Claim 25
Dependent Claim
81 words
Apparatus as defined in claim 19 wherein said factor is sufficient for suppression of said modulated video carrier to an extent that line synchronization at an unauthorized receiver is impossible due to peak inverted video signal portions having an amplitude more than that of synchronizing pulses amplitude modulated on said video carrier signal, and said synchronizing pulses have an amplitude insufficient to be detected by a television receiver, whereby totally false and time-varying information is derived from said suppressed video carrier.
Claim 26
Dependent Claim
30 words
Apparatus as defined in claim 19 wherein said factor is sufficient for suppression of said modulated video carrier in the range of about 50 to 100% of normal peak value.
Claim 27
Dependent Claim
22 words
Apparatus as defined in claim 19 wherein said factor is sufficient to suppress said modulated video carrier 75% of normal peak value.
Claim 28
Dependent Claim
125 words
Apparatus as defined in claim 19 wherein said means for transmitting information for use by authorized receivers to restore said suppressed video carrier to full peak level before normal processing comprises means for generating a reference subcarrier at a constant frequency, means for transmitting said reference subcarrier to all receivers receiving said suppressed video carrier, means for multiplying said reference subcarrier by a predetermined factor sufficient to produce an intermediate signal having a frequency which differs from the frequency of said video carrier signal by a predetermined amount, means for producing a reference carrier at a frequency equal to the difference between said intermediate signal and said video carrier signal, and means for transmitting said reference carrier to all receivers receiving said suppressed video carrier.
Claim 29
Dependent Claim
21 words
Apparatus as defined in claim 25 wherein said means for transmitting said reference subcarrier to all said receivers comprises a carrier.
Claim 30
Dependent Claim
33 words
Apparatus as defined in claim 25 wherein said means for transmitting said reference subcarrier to all said receivers comprises said audio carrier, and means for amplitude modulating said carrier with said reference subcarrier.
Claim 31
Dependent Claim
207 words
Apparatus as defined in claim 25 wherein an authorized receiver includes means for restoring said suppressed video carrier to full peak level before normal processing, said restoring means comprising means for continuously detecting said subcarrier reference, means for multiplying said detected subcarrier reference by said predetermined factor to produce a local intermediate signal of a frequency equal to the frequency of said intermediate signal employed to produce said reference carrier, means responsive to said reference carrier for producing a local carrier reference of a frequency which, when added to said local intermediate signal, is of the same frequency as said video carrier of said television program signal received, and converted as required whenever the received television program signal is being converted from one channel to another, means for adding said local reference carrier to said local intermediate signal to produce a local video carrier of the same frequency and phase as said suppressed video carrier converted as required, means for adjusting the amplitude of said local video carrier to restore said suppressed video carrier to its full peak level when added to said suppressed video carrier converted as required, and means for adding said amplitude adjusted local video carrier to said suppressed video carrier converted as required.
Claim 32
Dependent Claim
206 words
Apparatus as defined in claim 24 wherein said means for transmitting information for use by authorized receivers to restore said suppressed modulated video carrier to full peak level before normal processing comprises means for producing keying pulses synchronized with horizontal sync pulses in said video carrier, means for transmitting said keying pulses to all receivers receiving said suppressed video carrier, means at an authorized receiver for detecting said keying pulses and, in response to each keying pulse detected, for producing a gating pulse, means at said receiver for generating a local signal at a frequency of said suppressed video carrier converted as required whenever the received television program signal is being converted from one channel to another, means responsive to each gating pulse for gating a burst of said suppressed video carrier received, and converted as required, to said local signal generating means to synchronize the phase and frequency of said local signal with said suppressed video carrier received, and converted as required, means for adjusting the amplitude of said local signal to be sufficient to just restore said suppressed video carrier to its full peak level, and means for adding said amplitude adjusted local signal to said suppressed video carrier received, and converted as required.
Claim 33
Dependent Claim
17 words
Apparatus as defined by claim 29 wherein said means for transmitting said keying pulses comprises a carrier.
Claim 34
Dependent Claim
21 words
Apparatus as defined by claim 30 wherein said keying-pulse carrier is within the same television channel band as said video carrier.
Claim 35
Dependent Claim
34 words
Apparatus as defined in claim 30 wherein said keying-pulse carrier is said audio carrier, and said means for transmitting said keying pulses includes means for amplitude modulating said audio carrier with said keying pulses.
References Cited (Backward Citations)
USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-12-02 | 1978-06-03 | 1978-12-03 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-12-02 | 1982-06-03 | 1982-12-03 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-12-02 | 1986-06-03 | 1986-12-03 | $7700.00 | Window Closed / Lapsed |