System for multiplexing information channels adjacent to a video spectrum
AssigneeCoastcom
InventorsJ. Walter Johnson, Herbert H. Borchers
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Abstract
A system for multiplexing either a single or multiple information channels adjacent to the video spectrum on a TV microwave or cable by frequency modulating a high frequency subcarrier at wide deviation with one or composite information signals, translating the modulated subcarrier to a frequency adjacent to and above the video spectrum, and then bridging it into the video circuit at a level 20 dB or more below the peak video signal of the video spectrum. The system recovers the transmitted subcarrier from the video spectrum, synthesizes the subcarrier frequencies exclusive of most of the video interference in a limited bandwidth, and then detects the modulation of the synthesized subcarrier frequency.
Claims3
A method for recovering an information signal multiplexed with a video spectrum that includes sync pulses with the information signal being frequency modulated on a subcarrier having a center frequency and multiplexed with said video spectrum at a level at least 20 db below the peak level of said video spectrum so that the intermodulation products of the information signal and multiple harmonics of said sync pulses are at a level at least 45 db below said video spectrum, said method comprising the steps of:
- filtering the frequency modulated subcarrier and video spectrum to separate one from the other;
- synthesizing substantially only the frequency modulated subcarrier by tracking a portion of said modulated subcarrier adjacent to and including said center frequency of said subcarrier, said portion tracked including less than the full deviation of said modulated subcarrier to exclude said intermodulation products;
- and
- demodulating the synthesized modulated subcarrier.
An apparatus for recovering an information signal multiplexed with a video spectrum that includes sync pulses with the information signal being frequency modulated on a subcarrier with a center frequency and multiplexed with said video spectrum at a level at least 20 db below the peak level of said video spectrum so that the intermodulation products of the information signal and multiple harmonics of said video sync pulses are at a level at least 45 db below said video spectrum, said apparatus comprising:
- filter means to receive and separate said frequency modulated subcarrier and said video spectrum;
- a tracking filter for receiving the separated frequency modulated subcarrier and synthesizing substantially only the modulated subcarrier by tracking a portion of said modulated subcarrier adjacent to and including said center frequency of said subcarrier, said portion tracked including less than the full deviation of said modulated subcarrier to exclude said intermodulation products;
- and
- demodulator means for demodulating the synthesized modulated subcarrier.
Dependencies are inferred from the claim text.