| 摘要 |
PROBLEM TO BE SOLVED: To perform a mute operation optimum for the hearing of a user by detecting the state of a radio transmission line at each prescribed cycle and performing mute control to a voice output means corresponding to a detected result and a prescribed shifting condition between a mute operation and an un-mute operation. SOLUTION: The state of the radio transmission line is monitored in an SAT detection part 4 at each prescribed cycle, and SAT signals for indicating approval are not detected, a non-detection successive number counting part 5 increases the number of times of non-detection by one and continues the un-mute operation until a set maximum value is reached. At the point of time of reaching the maximum value, a mute control part 6 switches to the mute operation, also 0-clears a non-detection count value, returns to an initial operation and then repeats the similar operation. In such a manner, by capturing the deterioration of the radio transmission line and performing the mute operation at the point of time of the non-detection to a set maximum cycle without immediately performing the mute operation even when the SAT signals are not detected, unpleasant feelings by mute and noise are evaded as much as possible.
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