Radio frequency leakage detection system for CATV system

Abstract

A communication circuit carries at least one signal including synchronizing intervals by which output of the signal by first apparatus coupled to the communication circuit is to be synchronized. A communication method includes selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals. A modulator is provided for selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals. Another communication circuit carries at least a first signal including frequencies in at least a first frequency band. A method of determining whether the first signal is escaping from the circuit includes transporting along the circuit apparatus adapted for receiving the first signal, detecting whether a received signal includes frequencies in the first frequency band, and producing an indication that the received signal includes frequencies in the first frequency band. A detector is provided for transporting along the circuit for determining whether the first signal is escaping from the circuit. The detector is adapted for receiving the first signal, detecting whether a received signal includes frequencies in the first frequency band, and producing an indication that the received signal includes frequencies in the first frequency band.

1 . In a communication circuit which carries at least one signal including synchronizing intervals by which output of the signal by first apparatus coupled to the communication circuit is to be synchronized, a communication method including selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       2 . The method of  claim 1  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       3 . The method of  claim 1  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       4 . The method of  claim 3  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       5 . The method of  claim 3  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       6 . The method of  claim 5  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       7 . The method of  claim 5  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes generating a first sinusoid having a first frequency, generating a second sinusoid having a second frequency, frequency modulating the first sinusoid with the second sinusoid to produce a frequency modulated signal, and modulating at least a portion of the duration of at least some of the synchronizing intervals with the frequency modulated signal.  
   
   
       8 . The method of  claim 7  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       9 . The method of  claim 8  wherein detecting the modulation includes detecting the frequency modulated signal.  
   
   
       10 . The method of  claim 8  wherein detecting the modulation includes detecting the second sinusoid.  
   
   
       11 . The method of  claim 8  wherein detecting the modulation includes detecting the first sinusoid.  
   
   
       12 . The method of  claim 3  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of at least a portion of the duration of a relatively constant portion of the synchronizing intervals.  
   
   
       13 . The method of  claim 12  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       14 . The method of  claim 12  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating at least a portion of the duration of substantially all of the synchronizing intervals.  
   
   
       15 . The method of  claim 14  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       16 . The method of  claim 3  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes modulating the amplitude of substantially all of the duration of at least a portion of the synchronizing intervals.  
   
   
       17 . The method of  claim 16  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       18 . The method of  claim 16  wherein selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals includes sinusoidally modulating substantially all of the duration of at least a portion of the synchronizing intervals.  
   
   
       19 . The method of  claim 18  further including transporting along the circuit second apparatus adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       20 . In a communication circuit which carries at least one signal including synchronizing intervals by which output of the signal by first apparatus coupled to the communication circuit is to be synchronized, a modulator for selecting and modulating at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       21 . The apparatus of  claim 20  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       22 . The apparatus of  claim 20  wherein the modulator includes a modulator for selecting and modulating the amplitude of at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       23 . The apparatus of  claim 22  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       24 . The apparatus of  claim 22  wherein the modulator includes a modulator for sinusoidally modulating at least a portion of the duration of at least some of the synchronizing intervals.  
   
   
       25 . The apparatus of  claim 24  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       26 . The apparatus of  claim 24  wherein the modulator includes a modulator for generating a first sinusoid having a first frequency, generating a second sinusoid having a second frequency, frequency modulating the first sinusoid with the second sinusoid to produce a frequency modulated signal, and modulating at least a portion of the duration of at least some of the synchronizing intervals with the frequency modulated signal.  
   
   
       27 . The apparatus of  claim 26  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       28 . The apparatus of  claim 27  wherein the detector includes a detector for detecting the frequency modulated signal.  
   
   
       29 . The apparatus of  claim 27  wherein the detector includes a detector for detecting the second sinusoid.  
   
   
       30 . The apparatus of  claim 27  wherein the detector includes a detector for detecting the first sinusoid.  
   
   
       31 . The apparatus of  claim 22  wherein the modulator includes a modulator for modulating the amplitude of at least a portion of the duration of a relatively constant portion of the synchronizing intervals.  
   
   
       32 . The apparatus of  claim 31  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       33 . The apparatus of  claim 31  wherein the modulator includes a modulator for sinusoidally modulating at least a portion of the duration of substantially all of the synchronizing intervals.  
   
   
       34 . The apparatus of  claim 33  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       35 . The apparatus of  claim 22  wherein the modulator includes a modulator for modulating the amplitude of substantially all of the duration of at least a portion of the synchronizing intervals.  
   
   
       36 . The apparatus of  claim 35  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       37 . The apparatus of  claim 35  wherein the modulator includes a modulator for sinusoidally modulating substantially all of the duration of at least a portion of the synchronizing intervals.  
   
   
       38 . The apparatus of  claim 37  further including a detector for transportation along the circuit, the detector adapted for receiving the signal, detecting the modulation, and producing an indication that the modulation has been detected.  
   
   
       39 - 44 . (cancelled).