| 摘要 |
PROBLEM TO BE SOLVED: To reduce the effect of a noise and an unnecessary arriving wave by selectively receiving transmission radio waves whose frequencies are different, and optimally setting the reception frequency band of an intermediate frequency filter. SOLUTION: The reception signal of an antenna 11 is mixed with local oscillation frequencies from a local oscillator 29 by a frequency mixer 13 so that an intermediate frequency signal can be obtained, and this intermediate frequency signal is outputted through a changeover switch 21 to intermediate frequency filters 22 and 23. The intermediate frequency filters 22 and 23 select the intermediate frequency signal, and outputs it through a changeover switch 24 and a detector 16 to a PU 17. A switching timing generator 25 interlockingly switches changeover the switches 21 and 24, and outputs an intermediate frequency filter state signal 26 to the CPU 17. The CPU 17 confirms which of the intermediate frequency filters 22 and 23 is selected according to an intermediate frequency filter state signal 26, and outputs a changeover switch fixing instruction signal 27 to a switching timing generator 25 when detecting the received data, and continuously receives transmission radio waves. |
