| 摘要 |
PURPOSE:To obtain tuning to the center frequency of a received signal without using an expensive narrow-band-pass filter by confirming the frequency band of a received channel and then performing the tuning to the center received channel in the frequency band. CONSTITUTION:A control part 9 changes over oscillation frequencies of a local oscillation part 8 to starting channel selection at, for example, a lower-frequency channel. When a reception detection signal output from an intermediate amplification part 4 by a signal A is performed at frequencies (b), (c), and (d), the local oscillation part 8 is switched under the control of the control part 9 to obtain a reception detection signal of frequency (b) firstly. Then, the channel selecting operation is carried on at frequencies (c), (d), and (e) until the reception detection signal is ceased. The control part 9 stores the number N of reception detection signals and then the frequency is returned to the center channel to perform tuning. |
