| 摘要 |
PROBLEM TO BE SOLVED: To effectively transmit a state that a vehicle itself is in a weak field area of a receiving radio wave to a user without giving a feeling of wrongness or an unpleasant feeling to the user. SOLUTION: An RF signal (television signal) received through a first antenna 2 or a second antenna 3 and a diversity switching unit 4 is converted into an IF signal by a down converter 10 after passing an input filter 9. The IF signal is provided to a demodulator 13 through an IF signal amplifier 12 composed of a variable gain amplifier and provided also to a microcomputer 14 through a detector 15 and an A/D converter 16. When the level of a detection signal from the detector 15 is reduced to a previously set lower limit level or less, the microcomputer 14 controls the amplification factor of the IF signal amplifier 12 so as to forcedly reduce the amplification factor to a prescribed value (a value by which a display picture based on a video signal obtained by demodulating the IF signal becomes a sandstorm picture on which beat-like noise caused by external noise does not appear) or less. COPYRIGHT: (C)2007,JPO&INPIT
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