Radio frequency leakage detection system for CATV system

• US 5,608,428 A
• Filed: 06/09/1994
• Issued: 03/04/1997
• 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): Kostak, Victor R.
• Assistant Examiner(s): Hopkins, Martha J.
• Application Number:
  US08/257,198
• Time in Patent Office: 999 Days
• Field of Search: 348/6, 348/192, 348/193, 348/13, 348/180, 455/6.1, 455/14, 455/3.1, 333/237
• US Class Current: 725/149
• 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 a plurality of sources of program material, and a plurality of modulators for supplying a plurality of carrier frequency signals. Each modulator is modulated by a respective one of the sources of program material. Each of the program material sources is coupled to a respective modulator. The program material-modulated carrier frequencies are coupled in the circuit. Terminal apparatus is provided for demodulating at least one of the program material-modulated carrier frequency signals. The terminal apparatus includes automatic gain control (AGC) circuitry having an AGC bandwidth. The terminal apparatus is coupled to the circuit. One of the program material-modulated carrier frequencies is coupled in the circuit through a variable attenuator having an attenuator control signal input, a program material-modulated carrier frequency input, and a variably attenuated program material-modulated carrier frequency output. An oscillator generates at an oscillator output a signal having a frequency within the AGC bandwidth. Said one of the program material modulated carrier frequencies is coupled to the program material-modulated carrier frequency input. The oscillator output is coupled to the attenuator control signal input. The variably attenuated program material-modulated carrier frequency output is coupled in the circuit.

Claims

1. In a communication circuit comprising at least one source of program material, at least one modulator, a carrier frequency signal source for each of the modulators, means for coupling the program material sources to the modulators, means for coupling the program material-modulated carrier frequencies in the circuit, terminal apparatus for demodulating at least one of the program material-modulated carrier frequency signals, the terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, and means for coupling the terminal apparatus to the circuit, the improvement wherein the means for coupling one of the program material-modulated carrier frequencies in the circuit comprises a variable attenuator having a control input, a program material-modulated carrier frequency input, and a variably attenuated, program material-modulated carrier frequency output, an oscillator for generating at an oscillator output a signal having a frequency within the AGC bandwidth, means for coupling said one of the program material modulated carrier frequencies to the program material-modulated carrier frequency input, means for coupling the oscillator output to the control input, and means for coupling the variably attenuated, program material-modulated carrier frequency output in the circuit.

2. The improvement of claim 1 wherein the oscillator output signal frequency is less than about 35 Hz.

3. The improvement of claim 2 wherein the oscillator output signal frequency is in the range of from about 5 Hz to about 15 Hz.

4. The improvement of claim 1 further comprising a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of the leakage the variably attenuated, program material-modulated carrier frequency, for detecting in the variably attenuated, program material-modulated carrier frequency the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

5. The improvement of claim 4 wherein the oscillator output signal frequency is less than about 35 Hz.

6. The improvement of claim 5 wherein the oscillator output signal frequency is in the range of from about 5 Hz to about 15 Hz.

7. The improvement of claim 1, 2, 3, 4, 5 or 6 wherein the communication circuit comprises a CATV circuit and the terminal apparatus comprises at least one television receiver.

8. In a communication circuit, a method comprising the steps of providing at least one source of program material, providing at least one modulator, providing a carrier frequency signal source for each of the modulators, coupling the program material sources to the modulators, coupling the program material-modulated carrier frequencies in the circuit, providing terminal apparatus for demodulating at least one of the program material-modulated carrier frequency signals, the terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, and coupling the terminal apparatus to the circuit, the improvement comprising the steps of coupling one of the program material-modulated carrier frequencies in the circuit through a variable attenuator having a control input, a program material-modulated carrier frequency input, and a variably attenuated, program material-modulated carrier frequency output, providing an oscillator for generating at an oscillator output a signal having a frequency within the AGC bandwidth, coupling said one of the program material modulated carrier frequencies to the program material-modulated carrier frequency input, coupling the oscillator output to the control input, and coupling the variably attenuated, program material-modulated carrier frequency output in the circuit.

9. The improvement of claim 8 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency less than about 35 Hz.

10. The improvement of claim 9 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency in the range of from about 5 Hz to about 15 Hz.

11. The improvement of claim 8 further comprising providing a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of the leakage the variably attenuated, program material-modulated carrier frequency, for detecting in the variably attenuated, program material-modulated carrier frequency the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

12. The improvement of claim 11 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency less than about 35 Hz.

13. The improvement of claim 12 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency in the range of from about 5 Hz to about 15 Hz.

14. The improvement of claim 8, 9, 10, 11, 12 or 13 wherein the communication circuit comprises a CATV circuit and the step of providing terminal apparatus comprises the step of providing at least one television receiver.

15. In a communication circuit comprising at least one source of program material, at least one modulator, a carrier frequency signal source for each of the modulators, means for coupling the program material sources to the modulators, means for coupling the carrier frequency signal sources to the modulators, means for coupling the program material-modulated carrier frequencies in the circuit, terminal apparatus for demodulating at least one of the program material-modulated carrier frequency signals, the terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, and means for coupling the terminal apparatus to the circuit, the improvement wherein the means for coupling one of the program material-modulated carrier frequencies in the circuit comprises an amplitude modulator having a control input, a program material-modulated carrier frequency input, and an amplitude modulated, program material-modulated carrier frequency output, an oscillator for generating at an oscillator output a signal having a frequency within the AGC bandwidth, means for coupling said one of the program material modulated carrier frequencies to the program material-modulated carrier frequency input, means for coupling the oscillator output to the control input, and means for coupling the amplitude modulated, program material-modulated carrier frequency output in the circuit.

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

17. The improvement of claim 16 wherein the oscillator output signal frequency is in the range of from about 5 Hz to about 15 Hz.

18. The improvement of claim 15 further comprising a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of the leakage the amplitude modulated, program material-modulated carrier frequency, for detecting in the amplitude modulated, program material-modulated carrier frequency the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

19. The improvement of claim 18 wherein the oscillator output signal frequency is less than about 35 Hz.

20. The improvement of claim 19 wherein the oscillator output signal frequency is in the range of from about 5 Hz to about 15 Hz.

21. The improvement of claim 15, 16, 17, 18, 19 or 20 wherein the communication circuit comprises a CATV circuit and the terminal apparatus comprises at least one television receiver.

22. In a communication circuit, a method comprising the steps of providing at least one source of program material, at least one modulator, a source of carrier frequency signals for each of the modulators, coupling the program material sources to the modulators, coupling the program material-modulated carrier frequencies in the circuit, providing terminal apparatus for demodulating at least one of the program material-modulated carrier frequency signals, the terminal apparatus including automatic gain control (AGC) means having an AGC bandwidth, and coupling the terminal apparatus to the circuit, the improvement comprising the steps of coupling one of the program material-modulated carrier frequencies in the circuit through an amplitude modulator having a control input, a program material-modulated carrier frequency input, and an amplitude modulated, program material-modulated carrier frequency output, providing an oscillator for generating at an oscillator output a signal having a frequency within the AGC bandwidth, coupling said one of the program material modulated carrier frequencies to the program material-modulated carrier frequency input, coupling the oscillator output to the control input, and coupling the amplitude modulated, program material-modulated carrier frequency output in the circuit.

23. The improvement of claim 22 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency less than about 35 Hz.

24. The improvement of claim 23 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency in the range of from about 5 Hz to about 15 Hz.

25. The improvement of claim 22 further comprising providing a detector for receiving a signal representative of leakage from the communication circuit, for extracting from the signal representative of the leakage the amplitude modulated, program material-modulated carrier frequency, for detecting in the amplitude modulated, program material-modulated carrier frequency the oscillator output signal frequency, and for producing an indication of detection of the oscillator output signal frequency.

26. The improvement of claim 25 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency less than about 35 Hz.

27. The improvement of claim 26 wherein the step of providing an oscillator comprises the step of providing an oscillator having an oscillator output signal frequency in the range of from about 5 Hz to about 15 Hz.

28. The improvement of claim 22, 23, 24, 25, 26 or 27 wherein the communication circuit comprises a CATV circuit and the step of providing terminal apparatus comprises the step of providing at least one television receiver.