| 摘要 |
PURPOSE: To reduce the fluctuation of a frequency due to temperature change and to perform a stable operation by providing a local oscillation signal generator and supplying the local oscillation signal to a mixer based on a reference signal. CONSTITUTION: The mixer 2 generates an itermediate-frequency signal fIF by mixing a reception wave fRX with a local oscillation wave fLO, and demodulates it by a demodulator 3, and sends it out to a CPU 9. The CPU 9 controls the frequency fLO based on the intermediate-frequency signal fIF, and keeps the frequency fIF constant. Digital data is supplied to a D/A converter 6, and a prescribed control voltage Vc is generated. Thereby, the frequency is changed to the oscillation frequency fr of a VCXO 5 based on the control voltage Vc, and furthermore, the frequency fLO is changed. At this time, the CPU 9 monitors the intermediate-frequency fIF, and adjusts the digital data to be supplied to the converter 6 at an appropriate value. Also, the CPU 9 performs temperature compensation based on temperature data in an A/D converter 8, and performs control to keep the frequency fIF constant even when the temperature change occurs. |
