| 摘要 |
PURPOSE:To shorten the acquisition time of a satellite radio wave by performing searching while the frequency of a regenerated carrier wave is successively changed over a frequency interval wider than the capture range (CR) of a PLL until demodulation intensity reaches a predetermined level. CONSTITUTION:The same phase channel signal I and orthogonal channel signal Q demodulated by LPFs 4, 5 are inputted to a demodulation intensity calculation circuit 10 and respectively squared by square circuits 13, 14 to be inputted to a control circuit 11 as a demodulation intensity signal l=I<2>+Q<2>. At this time, when the position of the receiving frequency fc of a satellite radio wave is remotely separated from that of searching start frequency, the signals I, Q become 0 and the signal (l) also becomes 0. The circuit 11 monitors the signal (l) on the basis of a predetermined threshold value TH and, up to l> TH, the oscillation frequency of a voltage control oscillator (VCO) 8 is changed over at a frequency interval DELTAfw wider then the CR of a PLL and, when (l) becomes larger than TH, the circuit 11 detects this state to change over the frequency change-over interval of the VCO 8 from DELTAfw to the interval coinciding with the CR of the PLL. Therefore, the oscillation frequency of the VCO 8 can be allowed to approximate the vicinity of receiving frequency within a short time and a searching time can be shortened. |
