Colour television systems using at least one frequency-modulated subcarrier

Claim 1

A COLOUR TELEVISION SYSTEM OF THE TYPE WHEREIN THE TRANSMITTED COMPLEX VIDEO SIGNAL COMPRISES A FIRST WIDEBAND PICTURE SIGNAL, WHICH CAN BE USED BLACK AND WHITE RECEIVERS, AND AT LEAST ONE SUBCARRIER WAVE WHICH IS FREQUENCY-MODULATED BY A COLOUR SIGNAL, SAID SYSTEM COMPRISING: A TRANSMITTER COMPRISING A COLOUR CHANNEL INCLUDING: PRE-EMPHASIS MEANS HAVING AN INPUT FOR RECEIVING SAID COLOUR SIGNAL AND AN OUTPUT; A FREQUENCY MODULATOR HAVING A MODULATION INPUT COUPLED TO SAID PRE-EMPHASIS MEANS OUTPUT, AND AN OUTPUT; AND PHASE-PRECORRECTING MEANS HAVING AN INPUT COUPLED TO SAID FREQUENCY MODULATOR OUTPUT; AND A RECEIVER COMPRISING A COLOUR CHANNEL INCLUDING: A RECEIVER FILTER HAVING AN INPUT FOR RECEIVING SAID SUBCARRIER, AND AN OUTPUT, THE AMPLITUDE-FREQUENCY CHARACTERISTICS OF SAID RECEIVER FILTER SHOWING A MAXIMUM FOR A CENTRAL FREQUENCY OF THE BANDWIDTH OF SAID SUBCARRIER AND CONTINUOUSLY DECREASING ON BOTH SIDES THEREOF, SO THAT SAID AMPLITUDE-FREQUENCY CHARACTERISTIC DEFINES A FREQUENCY INTERVAL, REFERRED TO AS A "PROTECTED FREQUENCY INTERVAL," SUCH THAT SAID RECEIVER FILTER ATTENUATES TO A GREATER DEGREE A NOISE SIGNAL HAVING A UNIFORM ENERGY DISTRIBUTION WITHIN THE BANDWIDTH OF SAID SUBCARRIER THAN A WAVE HAVING A FREQUENCY LYING WITHIN SIAD PROTECTED FREQUENCY INTERVAL; A LIMITER HAVING AN INPUT COUPLED TO THE OUTPUT OF SAID RECEIVER FILTER AND AN OUTPUT; FREQUENCY DISCRIMINATING MEANS HAVING AN INPUT COUPLED TO SAID LIMITER OUTPUT, AND AN OUTPUT; AND DE-EMPHASIS MEANS HAVING AN INPUT COUPLED TO SAID FREQUENCY DISCRIMINATING MEANS OUTPUT,A ND AN OUTPUT; SAID PRE-EMPHASIS MEANS BEING MEANS FOR ATTENUATING THE LOWER FREQUENCY COMPONENTS OF SAID COLOUR SIGNAL RELATIVELY TO ITS HIGHER FREQUENCY COMPONENTS SO THAT THE INSTANTANEOUS FREQUENCY OF SAID SUBCARRIER WAVE IS INCLUDED, FOR MOST OF THE TIME, IN SAID PROTECTED FREQUENCY INTERVAL; SAID PHASE PRE-CORRECTING MEANS BEING MEANS FOR PRE-CORRECTING THE PHASE DISTORTION IMPARTED TO SAID SUBCARRIER BY SAID RECEIVER FILTER; SAID DE-EMPHASIS MEANS BEING MEANS FOR COMPENSATING FOR THE DISTORTION IMPARTED TO SAID COLOR SIGNAL BY SAID PRE-EMPHASIS MEANS.