Colour signal switching system of colour television receivers

Claim 1

A RECEIVER ADAPTED TO OPERATE IN A COLOUR TELEVISION SYSTEM WHEREIN THE COMPOSITE VIDEO SIGNAL COMPRISES A LUMINANCE SIGNAL AND A SUBCARRIER WHICH DURING THE ACTIVE FIELD PERIODS, IS ALTERNATELY MODULATED BY TWO COLOUR SIGNALS A1 AND A2 ALTERNATELY AT THE LINE FREQUENCY, AND WHICH, DURING CHECKING PERIODS, EACH OF WHICH IS INCLUDED IN A VERTICAL BLANKING INTERVAL, IS ALTERNATELY MODULATED BY TWO AUXILIARY SIGNALS, A1 AND A2, DESIGNATED INDENTIFICATION SIGNALS, ALTERNATING AT THE LINE FREQUENCY, EACH OF SAID IDENTIFICATION SIGNALS BEING IDENTICAL TO ITSELF FOR ANY TWO LINE PERIODS OF THE CHECKING PERIODS, AND THE TWO INDENTIFICATION SIGNALS BEING SUCH THAT THE DIFFERENCE A1-A2, THROUGHOUT A LINE PERIOD, HAS A SINGLE POLARITY; THE SELECTIVE TRANSMISSION OF A1 AND A2 DURING THE ACTIVE FIELD PERIODS, AND OF A1 AND A2 DURING THE CHECKING PERIODS, BEING EFFECTED RESPECTIVELY IN SYNCHRONISM WITH THE FIRST STATE AND SECOND STATE OF A TRANSMITTER SWITCH PASSING REGULARLY FROM ONE STATE TO ANOTHER AT LEAST BETWEEN THE BEGINNING OF EACH CHECKING PERIOD AND THE END OF THE NEXT ACTIVE FIELD PERIOD, SAID RECEIVER COMPRISING: A COLOUR CHANNEL FED WITH SAID SUBCARRIER, SAID COLOUR CHANNEL BEING SUBDIVIDED INTO TWO CHANNELS HAVING A COMMON INPUT AND RESPECTIVE OUTPUTS, ONE OF SAID TWO CHANNELS, DESIGNATED DELAY CHANNEL, COMPRISING A DELAY DEVICE IMPARTING TO THE SIGNALS PROPAGATED THERETHROUGH A DELAY, EQUAL TO THE DURATION OF A LINE PERIOD, RELATIVELY TO THE SIGNALS PROPAGATED THROUGH THE OTHER OF SAID TWO CHANNELS, DESIGNATED DIRECT CHANNEL; A RECEIVER SWITCH HAVING TWO SIGNAL INPUTS RESPECTIVELY COUPLED TO SAID OUTPUTS OF SAID DIRECT AND DELAY CHANNEL, AT LEAST ONE CONTROL INPUT, AND A FIRST AND A SECOND OUTPUT RESPECTIVELY ASSIGNED TO COLOUR SIGNALS A1 AND A2; SAID RECEIVER SWITCH, DURING THE ACTIVE FIELD PERIODS DIRECTING SIGNAL A1 TO ITS FIRST OUTPUT AND SIGNAL A2 TO ITS SECOND OUTPUT OR VICE VERSA ACCORDING TO WHETHER IT IS OR IT IS NOT IN THE SAME STATE; (I.E. FIRST STATE OR SECOND STATE) AS THE TANSMITTER SWITCH; A MATRIX HAVING TWO INPUTS RESPECTIVELY COUPLED TO THE OUTPUTS OF SAID RECEIVER SWITCH AND AN OUTPUT, SAID MATRIX BEING DESIGNED TO SUPPLY, DURING SAID CHECKING PERIODS, A SIGNAL REFFERED TO AS A TEST SIGNALS, WHICH IS EITHER OF THE FORM K(A1-A2) OR OF THE FORM -K(AL-A2), WHERE K IS A FACTOR HAVING A PREDETERMINED SIGN, ACCORDING TO WHETHER THE RECEIVER SWITCH IS OR IS NOT IN THE SAME STATE AS THE TRANSMITTER SWITCH; AND A RECEIVER SWITCH CONTROLLING CIRCUIT, HAVING AN INPUT COUPLED TO THE OUTPUT OF SAID MATRIX, SAID SWITCH CONTROLLING CIRCUIT COMPRISING FIRST MEANS FOR CAUSING THE RECEIVER SWITCH TO PASS REGULARLY FROM ONE STATE TO ANOTHER AT THE LINE FREQUENCY, AND CORRECTING MEANS CONTROLLED BY SAID TEST SIGNAL FOR, BETWEEN THE BEGINNINGS OF TWO SUCCESSIVE CHECKING PERIODS, EITHER LEAVING THE ACTION OF SAID FIRST MEANS TO PROCEED UNIMPAIRED, OR ON THE CONTRARY MODIFYING THIS ACTION, ACCORDING TO WHETHER, AT THE BEGINNING OF THE FIRST OF SAID TWO SUCCESSIVE CHECKING PERIODS, THE TEST SIGNAL HAS THE POLARITY, DESIGNATED CORRECT POLARITY, OF SIGNAL K(A1-A2) OF THE REVERSE POLARITY, DESIGNATED INCORRECT POLARITY.