System for multiplexing information channels adjacent to a video spectrum

• US 3,917,906 A
• Filed: 06/13/1973
• Issued: 11/04/1975
• Est. Priority Date: 06/13/1973
• Status: Expired due to Term

• Current Assignee: Herbert H. Borchers, Johnson J. Walter
• Original Assignee: Herbert H. Borchers, Johnson J. Walter
• Inventors: Johnson, J. Walter, Borchers, Herbert H.
• Primary Examiner(s): Griffin, Robert L.
• Assistant Examiner(s): Bookbinder, Marc E.
• Application Number:
  US05/369,481
• Time in Patent Office: 874 Days
• Field of Search: 178/5.6,5.8,5.2R,DIG.13,DIG.23 179/15FD,15BM,15AN 325/3,31,47,48,308,145,146,153,346
• US Class Current: 370/343
• CPC Class Codes: H04J 1/04 Frequency-transposition arrangements modulation with carrier or side-band suppression H03C1/52, H03C1/60; single-band suppression H04B1/00, H04B15/00; telegraphic communication H04L27/02, H04L25/49; transference of modulation from one carrier to another, e.g. frequency- changing H03D7/00; demodulation or transference of modulation of modulated electromagnetic waves H03D9/00
• CPC Class Codes: H04J 1/08 Arrangements for combining channels branching filters H01P1/213, H03H7/46
• CPC Class Codes: H04J 1/20 in which at least one carrier is angle-modulated H04J1/02 takes precedence; FM without multiplex H04B1/00, H04B14/006, H04B15/00; PSK H04L5/12; impulse-modulation without multiplex H04B14/02; time-division multiplexing for data transmission H04L5/22; telemetry G08C15/06 - G08C15/12; telephony H04Q11/00, H04Q11/04, H04Q11/0407
• CPC Class Codes: H04N 7/081 the additional information signals being transmitted by means of a subcarrier

Abstract

A system for multiplexing multiple information channels adjacent to the video spectrum on a TV microwave or cable unit 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.

Claims

1. A method for transmitting and recovering multiple channel information multiplexed with a video spectrum that includes sync pulses, said method comprising the steps of:

generating a video spectrum to be transmitted;

generating a plurality of information signals on multiple channels;

forming a composite signal from said information signals on said multiple channels;

generating a subcarrier having a center frequency greater than that of said video spectrum to be transmitted;

frequency modulating said subcarrier at a wide deviation ratio with said composite signal;

multiplexing said frequency modulated subcarrier above and adjacent to said video spectrum for simultaneous transmission, said modulated subcarrier being multiplexed at a level at least 20 db below the peak level of said video spectrum so that the intermodulation products of the modulated subcarrier and multiple harmonics of said video sync pulses are a level at least 45 db below said video spectrum;

transmitting said modulated subcarrier and video spectrum over a transmission channel of the microwave or cable type;

receiving said transmitted modulated subcarrier and video spectrum;

filtering the received signal to separate the modulated subcarrier from the video spectrum;

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

demodulating the synthesized modulated subcarrier.

2. The method of claim 1 wherein the information signals comprise a plurality of multiplexed single sideband supressed carrier information signals.

3. The method of claim 1 wherein the frequency modulated subcarrier is initially at a frequency greater than that of said video spectrum and is translated to a frequency above and adjacent to said video spectrum prior to said multiplexing with said video spectrum for better elimination of noise and spurious signals.

4. Apparatus for transmitting and recovering multiple channel information multiplexed with a video spectrum that includes sync pulses, said apparatus comprising:

circuit means for providing a video spectrum to be transmitted;

channel combining means for receiving information on a plurality of channels and providing a composite signal therefrom;

a modulator for receiving said composite signal from said channel combining means, said modulator frequency modulating said composite signal to provide a frequency modulated subcarrier having a center frequency greater than said video spectrum to be transmitted;

high impedance combining means for multiplexing said video spectrum and said modulated subcarrier from said modulator, said modulated subcarrier being multiplexed at a level at least 30 db below the peak level of said video spectrum so that the intermodulation products of the modulated subcarrier and multiple harmonics of said video sync pulses are at a level at least 45 db below said video spectrum;

transmitting means for transmitting said modulated subcarrier and video spectrum over a transmission channel of the microwave or cable type;

receiving means for receiving said transmitted Modulated subcarrier and video spectrum;

filter means for separating said modulated subcarrier from said video spectrum;

a tracking filter for receiving the separated 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.

5. A method for recovering multiple channel information multiplexed with a video spectrum that includes sync pulses with the multiple channel information 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 multiple channel information and multiple harmonics of said video 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.

6. An apparatus for recovering multiple channel information multiplexed with a video spectrum that includes sync pulses with the multiple channel information 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 multiple channel information 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.

7. The apparatus of claim 6 wherein the tracking filter is a phase locked loop having a local oscillator, the frequency of which is responsive to an applied error voltage, said local oscillator being normally at the subcarrier center frequency;

comparator means developing an error voltage proportional to the difference in phase between the instantaneous tracked subcarrier frequency and the frequency of the local oscillator;

means applying the error voltage within predetermined tracking limits to said local oscillator; and

means applying the local oscillator frequency to the demodulator means.