To reduce a judgment error on the presence or absence of the existence of a reception wave without being affected by noise even if noise exists in a band by extracting the signals of plural narrow bands by means of plural band pass filters, comparing the levels of the extracted signals with a prescribed threshold, and judging that the reception wave exists when the levels of all the signals exceed the threshold.
A spread spectrum communication signal f1 is amplified in an amplifier 3 and an RF signal from a transmission signal circuit 4 is mixed in a down converter 5. Thus, the signal is converted into an IF frequency and it is transmitted to the SAW band pass filters 7a-7d. Thus, signals f1-1 to f1-4 of the plural narrow bands are independently rectified by judgment circuits 8a-8d and a power level is judged by the prescribed threshold. When it is larger than the threshold, '1' is allocated. When it is smaller, '0' is allocated. The signals of '1' and '0' are AND-operated and the reception wave is judged to exist only when the value is '1'.
TANIMOTO KAZUHIRO
NEMOTO TSUYOSHI
KARASAWA KOICHI
