| 摘要 |
PURPOSE:To prevent a malfunction for switching an antenna in case when a receiving state has been deteriorated, by controlling the detection sensitivity of a multipath detection circuit according to a control signal which is generated in accordance with the level of a multipath noise. CONSTITUTION:When receiving by the antenna 8, if a multipath noise component appears in the detection output C, its output is transferred to the antenna switching circuit 1 as an antenna switching signal F through an HPF101, an amplifier 102, a detector 103, and a bistable multivibrator circuit 105. The circuit 1 switches the antenna to 9 from 8 in accordance with the instruction of the signal F. Subsequently, in case when the noise component has become large due to a remarkable deterioration of the receiving state, the level of detection output E of a detector 103 of the multipath detection circuit 10 is also increased and the output level G of the AGC voltage generating circuit 11 is increased. Accordingly, the gain of the amplifier 102 is decreased by said AGC voltage, and the detection sensitivity of the whole circuit 10 is lowered. As a result, the circuit 10 is operated frequently due to deterioration of the receiving state, and it is prevented to be an malfunction state. |
