Color television receiver employing both ambiguous and unambiguous index signals

Claim 1

IN A COLOR TELEVISION RECEIVER EMPLOYING AN INDEX TYPE CATHODE RAY RUBE WHEREIN COLORED LIGHT-EMISSIVE ELEMENTS AND INDEX ELEMENTS ARE SCANNED BY AN ELECTRON BEAM IN SUCCESSIVE LINE SCANS, MEANS FOR PRODUCING AN INDEX SIGNAL WHICH IS PHASE INVARIANT IN THE PRESENCE OF STRONG CHROMINANCE MODULATION OF SAID BEAM BUT WHICH IS NOT NECESSARILY INDICATIVE AT A PARTICULAR INSTANT OF BEAM POSITION RELATIVE TO ELEMENTS EMISSIVE OF LIGHT OF ONE COLOR, MEANS FOR PRODUCING AT LEAST AT THE BEGINNING OF EACH LINE SCAN A SECOND INDEX SIGNAL WHICH IS NECESSARILY INDICATIVE AT A PARTICULAR INSTANT OF BEAM POSITION RELATIVE TO ELEMENTS EMISSIVE OF LIGHT OF ONE COLOR, MEANS FOR DERIVING FROM SAID SIGNALS AN INDEX SIGNAL OF DESIRED FREQUENCY AND PHASE, THE PRESENCE OF LUMINANCE OR BRIGHTNESS BEAM MODULATION AT THE BEGINNING OF EACH LINE SCAN TENDING TO EFFECT ADVERSELY THE PHASE OF SAID DERIVED INDEX SIGNAL, AND MEANS FOR EFFECTIVELY REMOVING SAID MODULATION AT THE BEGINNING OF EACH LINE SCAN TO PREVENT ADVERSE EFFECT THEREOF UPON SAID DERIVED INDEX SIGNAL.