| 摘要 |
PURPOSE:To perform secure operation without the influence of a 4.5MHz sound carrier signal, by operating either of subcarrier oscillating circuits selectively on the basis of both combined outputs, i.e. the output of a multioscillating circuit whose oscillating operation is brought under on-off control according to whether a killer detection output is present or not and the output of a sound discriminating circuit which discriminates a sound carrier frequency. CONSTITUTION:The sound discriminating circuit 9 which discriminates between the carrier frequencies of a 4.5MHz and a 5.5MHz sound IF signal is provided together with an OR gate 10, and the oscillating operations of two subcarrier oscillating circuits 6 and 7 are switched on the basis of the mixed output of the oscillation output of an astable multioscillating circuit 8 and the discrimination output of the sound discriminating circuit 9. When a color television signal is received, a 3.5MHz subcarrier signal separated by a burst gate circuit 3 and a 3.58 subcarrier signal obtained by the subcarrier oscillating circuit 6 are supplied to a killer detection circuit 4 for killer detection and the oscillating operation of the astable multioscillating circuit 8 is stopped on the basis of the killer detection output obtained at this time. On the other hand, when a black-and-white television signal is received, no killer detection output is sent out of the circuit 4 even if a 4.5MHz sound carrier signal is outputted from the burst gate circuit 3 erroneously and supplied to the circuit 4 because the circuit 6 is in normal oscillating operation at this time, and consequently the amplifying operation of the 2nd band amplifier 2 is stopped to perform normal color killer operation. |
