Provided is a method for, upon transmission of a DSC message being instructed, enabling quick start of the transmission. The method includes; (1) instructing, upon transmission of the DSC message being instructed, an antenna tuner to start tuning regardless of whether being busy or not, and switching an antenna from reception to transmission after the tuning is completed, (2) performing busy check, and standing by for a time period defined in the standard, when a reception signal in a transmission channel is no longer a dot pattern, and executing these processes (1) and (2) in parallel.
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