Radio frequency leakage detection system for CATV system

• US 6,018,358 A
• Filed: 07/31/1996
• Issued: 01/25/2000
• Est. Priority Date: 06/09/1994
• Status: Expired due to Term

• Current Assignee: Trilithic Incorporated (Lumentum Holdings Inc.)
• Original Assignee: Trilithic Incorporated (Lumentum Holdings Inc.)
• Inventors: Bush, Terry W.
• Primary Examiner(s): Grant, Chris
• Application Number:
  US08/690,122
• Time in Patent Office: 1,273 Days
• Field of Search: 348/4, 348/5, 348/6, 348/12, 348/13, 348/192, 348/193
• US Class Current: 725/125
• CPC Class Codes: H04H 20/12 Arrangements for observation, testing or troubleshooting
• CPC Class Codes: H04H 20/78 CATV [Community Antenna Television] systems
• CPC Class Codes: H04N 7/10 Adaptations for transmission by electrical cable H04N7/12 takes precedence
• CPC Class Codes: H04N 7/102 Circuits therefor, e.g. noise reducers, equalisers, amplifiers H04N7/108 takes precedence

Abstract

A communication circuit comprises sources of program material, carrier frequency signal sources and first modulators for modulating the carrier frequency signal sources with the program material sources. Each of the first modulators has a first input terminal, a second input terminal and a first output terminal. Terminal apparatus for demodulating program material-modulated carrier frequency signals include automatic gain control (AGC) circuits having AGC bandwidths. One of the program material sources is coupled to the first input terminal of a respective first modulator through a second modulator having a third input terminal, a fourth input terminal and a second output terminal. A source of signals having a frequency in the AGC bandwidth is coupled to the third input terminal. The source of program material is coupled to the fourth input terminal. The second output terminal to the first input terminal.

Claims

1. A communication circuit comprising at least one source of program material, at least one carrier frequency signal source and at least one first modulator for modulating the at least one carrier frequency signal source with the at least one program material source, the at least one first modulator having a first input terminal, a second input terminal and a first output terminal, and at least one terminal apparatus for demodulating program material-modulated carrier frequency signals, the at least one terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, at least one first means for coupling the at least one program material source to the at least one first input terminal, at least one second means for coupling the at least one carrier frequency signal source to the at least one second input terminal, and at least one third means for coupling the at least one first output terminal to the at least one terminal apparatus, the at least one first coupling means comprising a second modulator having a third input terminal, a fourth input terminal and a second output terminal, a source of signals having a frequency in the AGC bandwidth, means for coupling the source of signals in the AGC bandwidth to the third input terminal, means for coupling the at least one source of program material to the fourth input terminal, and means for coupling the second output terminal to the first input terminal.

3. The apparatus of claim 1 or 2 wherein the source of signals having a frequency in the AGC bandwidth comprises an oscillator having an output signal frequency less than about 35 Hz.

4. The apparatus of claim 3 wherein the oscillator output signal frequency is in the range of from about 3 Hz to about 15 Hz.

5. The apparatus of claim 4 and further comprising a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of leakage the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

6. The apparatus of claim 3 and further comprising a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of leakage the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

7. The apparatus of claim 1 or 2 and further comprising a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of leakage signals in the AGC bandwidth, and for producing an indication of detection of signals in the AGC bandwidth.

2. A communication circuit comprising at least one source of program material, at least one carrier frequency signal source and at least one first modulator for modulating the at least one carrier frequency signal source with the at least one program material source, the at least one first modulator having a first input terminal, a second input terminal and a first output terminal, and at least one terminal apparatus for demodulating program material-modulated carrier frequency signals, the at least one terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, at least one first means for coupling the at least one program material source to the at least one first input terminal, at least one second means for coupling the at least one carrier frequency signal source to the at least one second input terminal, and at least one third means for coupling the at least one first output terminal to the at least one terminal apparatus, the at least one second coupling means comprising a second modulator having a third input terminal, a fourth input terminal and a second output terminal, a source of signals having a frequency in the AGC bandwidth, means for coupling the source of signals in the AGC bandwidth to the third input terminal, means for coupling the at least one carrier frequency signal source to the fourth input terminal, and means for coupling the second output terminal to the second input terminal.

8. A communication method comprising the steps of providing at least one source of program material, at least one carrier frequency signal source, modulating the at least one carrier frequency signal source with the at least one program material source in at least one first modulator, demodulating program material-modulated carrier frequency signals in at least one terminal apparatus, providing the at least one first modulator with a first input terminal, a second input terminal and a first output terminal, providing the at least one terminal apparatus with automatic gain control (AGC) means having an AGC bandwidth, coupling the at least one program material source to the at least one first input terminal through at least one first means, coupling the at least one carrier frequency signal source to the at least one second input terminal through at least one second means, coupling the at least one first output terminal to the at least one terminal apparatus through at least one third means, the at least one first coupling means comprising a second modulator, providing on the second modulator a third input terminal, a fourth input terminal and a second output terminal, providing a source of signals having a frequency in the AGC bandwidth, coupling the source of signals in the AGC bandwidth to the third input terminal, coupling the at least one source of program material to the fourth input terminal, and coupling the second output terminal to the first input terminal.

10. The method of claim 8 or 9 wherein the step of providing a source of signals having a frequency in the AGC bandwidth comprises providing an oscillator having an output signal frequency less than about 35 Hz.

11. The method of claim 10 and further comprising receiving a signal representative of leakage from the communication circuit, extracting from the signal representative of leakage the oscillator output signal frequency, and producing an indication of detection of the oscillator output signal frequency.

12. The method of claim 10 wherein the step of providing an oscillator having an output signal frequency less than about 35 Hz comprises providing an oscillator having an output signal frequency in the range of from about 3 Hz to about 15 Hz.

13. The method of claim 12 and further comprising receiving a signal representative of leakage from the communication circuit, extracting from the signal representative of leakage the oscillator output signal frequency, and producing an indication of detection of the oscillator output signal frequency.

14. The method of claim 8 or 9 and further comprising receiving a signal representative of leakage from the communication circuit, extracting from the signal representative of leakage signals in the AGC bandwidth, and producing an indication of detection of signals in the AGC bandwidth.

9. A communication method comprising the steps of providing at least one source of program material, at least one carrier frequency signal source, modulating the at least one carrier frequency signal source with the at least one program material source in at least one first modulator, demodulating program material-modulated carrier frequency signals in at least one terminal apparatus, providing the at least one first modulator with a first input terminal, a second input terminal and a first output terminal, providing the at least one terminal apparatus with automatic gain control (AGC) means having an AGC bandwidth, coupling the at least one program material source to the at least one first input terminal through at least one first means, coupling the at least one carrier frequency signal source to the at least one second input terminal through at least one second means, coupling the at least one first output terminal to the at least one terminal apparatus through at least one third means, the at least one second coupling means comprising a second modulator providing on the second modulator a third input terminal, a fourth input terminal and a second output terminal, providing a source of signals having a frequency in the AGC bandwidth, coupling the source of signals in the AGC bandwidth to the third input terminal, coupling the at least one carrier frequency signal source to the fourth input terminal, and coupling the second output terminal to the second input terminal.

15. A communication circuit comprising n sources of program material, where n is an integer, n+1 carrier frequency modulators, n+1 sources of carrier frequency signals, each of the n program material sources and n of the n+1 carrier frequency signals being coupled to carrier frequency modulators, the n program material sources thereby modulating n of the carrier frequency signals to provide n output signals, terminal apparatus for recovering the program material selectively from the output signals, the terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, and an oscillator having a frequency in the AGC bandwidth, the oscillator and the (n+1)st carrier frequency being coupled to the (n+1)st carrier frequency modulator to modulate the (n+1)st carrier frequency by the oscillator frequency, and a detector for receiving a signal representative of leakage of the thus-modulated (n+1)st carrier frequency from the circuit, for detecting the oscillator output frequency in the received signal, and for producing an indication of detection of the oscillator output frequency.

16. The apparatus of claim 15 wherein the oscillator output frequency is less than about 35 Hz.

17. The apparatus of claim 16 wherein the oscillator output frequency is in the range of from about 3 Hz to about 15 Hz.

18. The apparatus of claim 15, 16 or 17 wherein the communication circuit comprises a CATV circuit and the terminal apparatus comprises at least one television receiver.

19. In a communication circuit, a method comprising the steps of providing n sources of program material, where n is an integer, n+1 carrier frequency modulators, n+1 sources of carrier frequency signals, coupling each of the n program material sources and n of the n+1 carrier frequency signals to carrier frequency modulators, thereby modulating n of the carrier frequency signals with the n program material sources to provide n output signals, recovering the program material selectively from the output signals with terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, coupling an oscillator having a frequency in the AGC bandwidth and the (n+1)st carrier frequency to the (n+1)st carrier frequency modulator to modulate the (n+1)st carrier frequency by the oscillator frequency, receiving a signal representative of leakage of the thus-modulated (n+1)st carrier frequency from the circuit, detecting the oscillator output frequency in the received signal, and producing an indication of detection of the oscillator output frequency.

20. The method of claim 19 wherein coupling an oscillator having a frequency in the AGC bandwidth to the (n+1)st carrier frequency modulator comprises coupling an oscillator having a frequency less than about 35 Hz to the (n+1)st carrier frequency modulator.

21. The method of claim 20 wherein coupling an oscillator having a frequency in the AGC bandwidth to the (n+1)st carrier frequency modulator comprises coupling an oscillator having a frequency in the range of from about 3 Hz to about 15 Hz to the (n+1)st carrier frequency modulator.

22. The method of claim 19, 20 or 21 wherein recovering the program material selectively from the output signals with terminal apparatus including AGC means comprises recovering the program material with at least one television receiver.