| 摘要 |
PROBLEM TO BE SOLVED: To precisely detect an antenna in a well receiving state and to suppress erroneous control to antenna switching. SOLUTION: Noise is detected by allowing a comparator 15 to compare noise components Sn obtained from a presently selected antenna with a threshold THD. When noise prescribed number of times Nmax is detected within a prescribed time Tns, an antenna switch control unit 17 outputs an antenna switch control signal Sv to switch to another antenna. When all the antennas are switched within a prescribed time Tchn, a number of noise-witching times analytic part 18 judges that the threshold THD has to be changed, and outputs a sensitivity control signal Sx. When the sensitivity control signal Sx is supplied within a prescribed timeτ, a noise detecting sensitivity setting part 19 degrades the noise detecting sensitivity of the comparator 15 by raising the threshold THD. When the sensitivity control signal Sx is not supplied through the prescribed timeτhas passed, the setting part 19 raises the noise detection sensitivity of the comparator 15 by lowering the theshold THD. Thus, by raising and lowering noise detecting sensitivity corresponding to whether an actual receiving state is good or not, the antenna in the well receiving state is detected precisely and erroneous control to the antenna switch is suppressed.
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