Method and apparatus for secure audio channel transmission in a CATV system
First Claim
1. A method for the secure transmission of audio information in a system for the transmission of associated television audio and video information comprising the steps ofpicking up the associated audio and video information,transmitting the video information as a conventional television signal in a conventional television channel,wherein the audio information is secured by transmitting the audio information as an FM signal at a radio frequency which is a subharmonic of a frequency in the conventional FM broadcast band and is outside said band, andreceiving the FM signal at a frequency converter and converting the FM signal'"'"'s frequency to a frequency in the conventional FM radio broadcast band for reception by a conventional FM broadcast band radio receiver.
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Accused Products
Abstract
A secure audio channel transmission system method and apparatus in which an FM signal is generated on an FM broadcast frequency, such as 107.5 megahertz, divided in frequency by 2 and distributed via a cable television system to subscribers equipped with frequency doubler circuits that reconstitute the FM signal for reception on a standard FM broadcast receiver. Unauthorized reception is prevented by the use of the non-standard, frequency-divided signal which is not receivable by standard broadcast channel television or FM receivers.
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Citations
13 Claims
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1. A method for the secure transmission of audio information in a system for the transmission of associated television audio and video information comprising the steps of
picking up the associated audio and video information, transmitting the video information as a conventional television signal in a conventional television channel, wherein the audio information is secured by transmitting the audio information as an FM signal at a radio frequency which is a subharmonic of a frequency in the conventional FM broadcast band and is outside said band, and receiving the FM signal at a frequency converter and converting the FM signal'"'"'s frequency to a frequency in the conventional FM radio broadcast band for reception by a conventional FM broadcast band radio receiver.
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9. Apparatus for the secure transmission of audio information in a system for transmission of associated television audio and video information comprising
at least one audio signal source, a video transmitter for producing a first RF signal in the television broadcast band, the first RF signal being modulated by the output of the video signal source, at least one audio signal source, an audio transmitter for producing a second RF signal at a frequency outside of the conventional broadcast bands, the second RF signal being at a subharmonic of a frequency in the conventional FM broadcast band and the second RF signal being modulated by the output of the audio signal source, combiner means for combining the first RF signal and the second RF signal on a common transmission system, converter means at a receiving location on said common transmission system for converting the second RF signal to the frequency in the FM broadcast band, and a conventional FM broadcast band radio receiver.
Specification