| 摘要 |
PROBLEM TO BE SOLVED: To prevent a disturbance signal from an adjacent signal and to demodulate a desired signal. SOLUTION: A frequency conversion circuit 4 converts an input signal from an antenna 2 into a 1st intermediate frequency signal with a 1st intermediate frequency higher than the frequency of a demodulated signal by 57 MHz. A frequency conversion circuit 8 converts the 1st intermediate frequency signal into a 2nd intermediate frequency signal with a 2nd intermediate frequency. The 2nd intermediate frequency is lower than the incremented frequency of 57 MHz of the 1st intermediate frequency that is higher than the frequency of the demodulated signal by a half of the frequency of an FET sampling clock. A clock generating circuit 11 generates a signal with a frequency twice that of the FFT sampling clock, that is, four times that of the 2nd intermediate frequency. An A/D converter circuit 10 samples the 2nd intermediate frequency signal on the basis of a signal fed from the clock generating circuit 11, a demodulation circuit 12 demodulates the sampled signal, and an FFT circuit 13 applies FFT to the demodulated signal.
|
