To solve the problem that it takes a certain amount of time to decide a band, the optimum band is not instantly selected, and if a low-level signal is inputted during selecting a wide band, the signal cannot be captured because the widest band equipped in a receiving apparatus is firstly set to analyze the radio wave, and the optimum band is selected when receiving a radio wave having unidentified bandwidth.
A received radio wave is distributed by a distributor 1, and inputted into three filters 2, 3, 4 having different bandwidths. The outputs of the filters 2, 3, 4 are detected with a detector 6, and an S/N ratio of each system is compared by an S/N ratio determining circuit 8. The determining circuit is previously caused to store a noise level at the time of no signal. A switch 9 is controlled so as to select a system having the highest S/N ratio. To prevent an input signal to pass through while the determining circuit is performing determination, a delay line 10 for delaying just for a delay time required for determining by the circuit 8 is inserted so that the signal may pass through after the switch 9 selects a system.
Toshihide Kodama
Takenaka Ikuo
Keigo Murakami
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