| 摘要 |
A transmit-receive system is composed of a portable transmitter-receiver and an external transmitter-receiver that exchange data by using air-propagating signals. The portable unit has a start switch, and transmits a start signal to the external unit when the start switch is turned on. Upon receiving the start signal, the external unit transmits a question signal to the portable unit. Upon receiving the question signal, the portable unit transmits thereto a response signal. Optionally, the external unit intermittently transmits the question signal, and becomes ready to receive during the question signal intermission. The external unit stops transmission of the question signal if it transmits the question signal a predetermined number of times without receiving the response signal. Further, the external unit intermittently becomes ready to receive for periods shorter than the question signal intermission.
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