Tagging digital television signals

Abstract

A method and apparatus for detecting leakage of a digital CATV channel signal from a CATV system. The digital CATV channel signal is amplitude modulated with a tag signal having a frequency in the range of about 3 Hz to about 35 Hz, and coupled to the CATV system. At a point of leakage from the CATV system, the amplitude modulated digital CATV channel signal can be detected using a leakage detector capable of recovering the tag signal.

1 - 34 . (canceled) 
     
     
         35 . A CATV system comprising:
 a source of program material;   a digital modulator for modulating the program material into a digital television signal;   a channel modulator coupled to the digital modulator for modulating the digital television signal to a CATV channel frequency;   an amplitude modulator coupled to the channel modulator for amplitude modulating the CATV channel frequency signal; and,   a CATV plant coupled to the amplitude modulator for distributing the amplitude modulated CATV channel frequency signal.   
     
     
         36 . The system of  claim 35  wherein the amplitude modulator modulates the cable channel frequency signal at a rate of between about 3 Hz and about 35 Hz. 
     
     
         37 . The system of  claim 36  wherein the amplitude modulator modulates the cable channel frequency signal at a rate of between about 10 Hz and about 23 Hz. 
     
     
         38 . The system of  claim 35  wherein the amplitude modulator modulates the cable channel frequency signal to a depth of between about 0.5 dB and 5 dB. 
     
     
         39 . The system of  claim 38  wherein the amplitude modulator modulates the cable channel frequency signal to a depth of between about 1 dB and about 3 dB. 
     
     
         40 - 77 . (canceled)