| 摘要 |
881,608. Tuning indicator arrangements; automatic frequency control systems. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 28, 1960 [May 1, 1959], No. 14942/60. Class 40(5). A colour television receiver for a signal comprising a carrier modulated with a brightness component and also with a component comprising a subcarrier modulated with colour signals, comprises a first I.F. amplifier coupled to a detector for the brightness component and a second separate I.F. amplifier coupled to a further detector for the colour signals, in which the circuit of this further detector includes a resonant circuit for deriving the main carrier, which is used for tuning indication or automatic frequency control. A preliminary I.F. amplifier 40 feeds in parallel I.F. amplifiers 41, 42, the amplifier 41 feeding the luminence detector 50. The amplifier 42 feeds via transformer 45 into a circuit 55, 56 tuned to the colour sub-carrier I.F. frequency which feeds the detector 57. Across the circuit 55, 56 is connected by condenser 61 a circuit 62 tuned to the I.F. corresponding to the main carrier which is applied to a detector (Fig. 2, not shown) which is coupled to a tuning indicator tube by way of a D.C. amplifier. The circuit 62 may alternatively form part of a frequency-discriminator (Fig. 3, not shown) which is followed by a cathode follower and controls the frequency of the local oscillator. The arrangement prevents interaction between the circuit 62 tuned to the main carrier intermediate frequency and the I.F. circuits feeding the luminescence detector. |
