| 摘要 |
PURPOSE:To simplify the constitution of a channel selection circuit and to attain the assured automatic discrimination of a broadcast system, by switching an IF selecting circuit which discriminates the broadcast system from the inter-carrier component obtained through an IF amplification/wave detection circuit. CONSTITUTION:A VHF low channel of a CCIR-B system is selected by a channel selection circuit main body 10 and converted into IF signals by an electronic tuner circuit 1. These IF signals are applied to an IF selecting circuit 2 and a tuning circuit 8. A sound carrier wave of the CCIR-B system is extracted through the circuit 8 at a prescribed level and applied to an OR circuit 11. The IF signal selected by the circuit 2 is applied to the circuit, and added with the sound carrier wave. The output of the circuit 11 is applied to an IF amplification/wave detection circuit 3, and the signal amplified and wave detected by the circuit 3 is applied to a discrimination circuit 7. The circuit 7 discriminates that a channel of the CCIR-B system is selected. Then the circuit 3 is controlled to select the IF signal assuredly out of the circuit 11. Thus the automatic discrimination is possible for a broadcast system with a simple circuit constitution.
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