PROBLEM TO BE SOLVED: To correctly detect a Nyquist point, even if a detection signal becomes equal to a planned symbol convergence value deviates by a large amount in time from the Nyquist point, by omitting offset correction or normalization in a 4-value FSK (frequency shift keying) portable terminal 10.;SOLUTION: A single-symbol period is divided equally, the equally divided points are each set at a sampling point, and a sampling point sequence is associated with the each of the equally divided points. A subtractor 30 and a one-sample delay circuit 31 constitute a differentiation circuit and supply a differentiated value of the detection signal at each sampling point to an absolute-value calculating section 32. The absolute-value calculating section 32 calculates the absolute value of the derivative value and outputs the calculated absolute value to a waveform averaging section 33. The waveform averaging section 33 calculates the mean value of the absolute values per sampling point sequence during n-sets of continuous symbol periods. A Nyquist point determining section 34 sets as a Nyquist point a sampling point corresponding to the sampling point sequence in which the mean value becomes a minimum.;COPYRIGHT: (C)2011,JPO&INPIT
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