| 摘要 |
A reference electrical signal oscillated by the main oscillator ( 11 ) has two kinds of frequencies (f<SUB>1</SUB>, f<SUB>2</SUB>) which are different from each other and any one of which is alternatively selected, a sampling signal is synchronized with the reference electrical signal once every n times, and a frequency (f<SUB>s</SUB>) of the sampling signal is an average value of the two kinds of frequencies (f<SUB>1</SUB>, f<SUB>2</SUB>) of the reference electrical signal, and the A/D conversion portion carries out at least one A/D conversion per period of the reference electrical signal and the received electrical signal based on the sampling signal.
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