Audio encoding/decoding system for catv
阅读：29发布：2023-05-11
专利汇可以提供Audio encoding/decoding system for catv专利检索，专利查询，专利分析的服务。并且In a Community Antenna Television (CATV) System, a system for hiding the audio portion of a television program from unauthorized television receivers connected to the CATV distribution system, is provided by converting the video carrier frequency to another frequency whereby intercarrier demodulation at a receiver, which is necessary to recover the audio program, cannot be accomplished. Provision is made at authorized receivers for restoring the video and audio carriers to their proper relative frequency locations.，下面是Audio encoding/decoding system for catv专利的具体信息内容。
1. In a CATV system of a type wherein, in unencoded form a television channel has a video carrier at a predetermined frequency at a standard location within the channel which is separated in frequency from an audio carrier, also at a predetermined frequency at a standard location within the channel by a predetermined amount for intercarrier demodulation by subscriber receivers, a method of preventing audio from being intelligibly reproduced by an unauthorized subscriber receiver of the type using intercarrier demodulation for recovering the audio and for maintaining the audio recoverable by an authorized subscriber receiver, unaffected by adjacent CATV television channel signals comprising: generating an audio carrier having said predetermined frequency, generating a video carrier having a frequency which differs from said predetermined video frequency and which is separated from the frequency of the audio carrier by a predetermined amount which prevents intercarrier demodulation by said unauthorized subscriber receivers, said video carrier being substantially 1.5 MHz below the high end of said television channel, modulating audio signals on said audio carrier, modulating video signals on said video carrier, and transmitting said audio and video modulated on their respective carriers to said receivers.
2. In a CATV system as recited in claim 1 wherein said audio carrier frequency is 0.25 MHz below the high end of the television channel and said video IF carrier frequency is 1.5 MHz below the high end of the television channel.
3. In a CATV system of a type wherein, in unencoded form a television IF channel has a video IF carrier at a predetermined frequency location which is separated in frequency from an audio IF carrier, also aT a predetermined frequency location by a predetermined amount for intercarrier demodulation by subscriber receivers, a method of preventing audio from being intelligibly reproduced by an unauthorized subscriber receiver of the type using intercarrier demodulation for recovering the audio and for maintaining the audio recoverable by an authorized subscriber receiver, undisturbed by adjacent CATV television channel signals comprising: generating an audio IF carrier at said predetermined frequency location within a television channel, generating a video IF carrier at a frequency which is less than 4.5 MHz different from the audio carrier IF frequency within said television channel, modulating audio signals on said audio IF carrier, modulating video signals on said video IF carrier, and transmitting said audio and video modulated on their respective IF carriers to said receivers.
4. In a CATV system as recited in claim 3, the method of recovering said audio comprising: receiving said transmitted audio and video signals respectively modulated on audio and video carriers, converting said received audio and video carriers to intermediate frequencies wherein the video IF carrier is at said predetermined frequency location within a television channel and the audio IF carrier is at a frequency lower than said video IF carrier and separated from said video IF carrier by the same frequency differences as existed between said received audio and video carriers, transposing said audio IF carrier to a frequency which is separated 4.5 megacycles from the frequency of said video IF carrier, and heterodyning said audio and video IF carriers with a signal having a frequency which enables reception and intelligible use by a television receiver.
5. In a CATV system as recited in claim 3, the method of recovering said audio comprising: receiving said transmitted audio and video signals respectively modulated on audio and video carriers, transposing said audio carrier to an intermediate frequency which is 0.25 MHz above the frequency of the low end of the IF channel, and heterodyning both said audio and video IF carriers with a signal having a frequency which transposes said video IF carrier to a predetermined frequency within a television channel and said audio IF carrier to a frequency 4.5 MHz above said video carrier frequency.
6. In a CATV system of the type wherein in unencoded form a television channel has an audio IF carrier at a predetermined frequency location and a video IF carrier at a predetermined frequency location 4.5 MHz higher than said audio IF carrier, means for preventing audio from being intelligibly reproduced by an unauthorized subscriber receiver and for enabling recovery of said audio by authorized subscriber receivers unmodulated by adjacent CATV television channel signals comprising: a source of audio signals, means for generating an audio IF carrier having said predetermined frequency, means for modulating said audio IF carrier with said audio signals, a source of video signals, means for generating a video IF carrier having a frequency less than 4.5 MHz apart yet higher in frequency than the frequency of said audio IF carrier, means for modulating said video IF carrier with said video signals, and means for transmitting said audio modulated on an audio IF carrier and said video modulated on a video IF carrier to subscriber receivers.
7. In a CATV system as recited in claim 6 wherein the frequency of said video IF carrier is 1.25 MHz above the frequency of said audio IF carrier.
8. In a CATV system of the type having transmitter means for generating a carrier signal for a television channel having modulated thereon a video carrier and an audio carrier, the frequency of said video carrier being spaced less than 4.5 MHz Distant from the frequency of said audio carrier, and said video carrier being displaced from its customary frequency location, a decoder comprising: intermediate frequency means for removing the channel carrier while maintaining the IF carrier frequencies of said video carrier and audio carrier within said television channel without changing their relative frequency separation, first oscillator means, first means for heterodyning said audio IF carrier with the output of said first oscillator means for transposing said audio carrier IF frequency to a frequency spaced 4.5 MHz from that of said video IF carrier, second oscillator means, and second means for heterodyning said video IF carrier and said transposed audio IF carrier with the output of said second oscillator means for transposing them to frequencies which can be utilized by a television receiver.
9. Apparatus as recited in claim 8 wherein said intermediate frequency means includes means for converting said video carrier and said audio carrier to a first intermediate frequency channel wherein said first video IF carrier and first audio IF carrier are at relatively higher frequencies than said audio and video carrier frequencies, said relatively higher frequency being on the low frequency end of said IF channel, and means for converting said first audio IF carrier and said first video IF carrier respectively to a second audio IF carrier and a second video IF carrier which are lower in frequency than the first audio IF carrier and first video IF carrier and which are located near the higher frequency end of a second intermediate frequency television channel created by said last named means for converting.
10. In a CATV system of the type having transmitter means for generating a carrier signal for a television channel having modulated thereon a video carrier and an audio carrier, the frequency of said video carrier being spaced less than 4.5 MHz distant from the frequency of said audio carrier, and said video carrier being displaced from its customary frequency location, a decoder comprising: intermediate frequency means for converting said video and audio carriers respectively to intermediate frequency carriers without changing their relative frequency separation, an adder circuit to which the output of said intermediate frequency means is applied, first oscillator means, a first means, to which the output of said intermediate frequency means is applied for selectively heterodyning the output of said first oscillator means with said audio IF carrier for transposing said audio IF carrier to a frequency spaced 4.5 MHz from that of said video IF carrier, means for applying the output of said first means for selectively heterodyning to said adder to be added to the output of said intermediate frequency means, a trap means connected to the output of said adder circuit for removing therefrom any audio IF carrier received from said intermediate frequency means, second oscillator means, and second means for heterodying the outputs of said adder circuit with the output of said second oscillator means for transposing them to frequencies which can be utilized by a subscriber television receiver.
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