| 摘要 |
PROBLEM TO BE SOLVED: To remove influence due to interfering waves (26 to 30 MHz) for immunity test, which are especially influential to VHF low band and causes noises in a demodulated audio signal an, where a down conversion scheme is employed for an audio demodulation circuit of L system. SOLUTION: An audio processing circuit 20 includes a local oscillation circuit 8 and a mixer 7 for down-converting an audio intermediate frequency signal from a tuner to a second audio intermediate frequency signal of low frequency for audio demodulation. The local oscillation circuit 8 outputs a local oscillation signal of a frequency higher than the audio intermediate frequency by 6.5 MHz, upon the receipt of a VHF low-band channel of L system and outputs a local oscillation signal in phase-synchronization with a video intermediate frequency signal upon the receipt of other band channels.
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