| 摘要 |
PURPOSE:To perform antenna switching operation only when it is necessary and to reduce antenna switching noises by starting retrieving operation in response to the generation of a noise and searching for and selecting an antenna which has a large received electric field among plural antennas. CONSTITUTION:If a noise component is generated in the output of a level detecting circuit 7a, a monostable multivibrator 14 operates to supply a trigger signal to a pulse generating circuit 16. In an intermediate or intense electric field, the pulse generating circuit 16 is triggered to enable an antenna 1 or 2 which has large received electric field intensity to be searched for according to the trigger signal. An antenna switching driving circuit 56 switches an antenna selecting circuit 3 according to the level comparison result of a level comparing circuit 55 to select an antenna with a high reception level automatically.
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