DEMODULATOR FOR SPREAD SPECTRUM SIGNAL

摘要

PURPOSE:To obtain a conversion PN lock state by controlling an oscillating frequency of a VCO for doppler shift lock so as to be fixed to a prescribed value when an output level of a BPF reaches a prescribed value or below. CONSTITUTION:A CPU8 has a switch means 25 controlled switchingly by an envelope output confirming signal EVH as a control signal DPC to a doppler shift lock VCO10. The means 25 transmits a normal control signal NOR as a control signal DPC when an envelope detection output ENV is a threshold value Lth or over and transmits a forced control signal REF as a control signal DPC because of the absence of an envelope output confirming signal EVH when the detected output ENV is a value Lth or below. The signal REF is selected in advance to a value at which the VCO10 oscillates at a center frequency f0 of a foced frequency range VOCf. Thus, the frequency of the signal PSS is kept within the pass band of a BPF11 when the VCO10 and 15 are transited from the force control state to the normal control state and the doppler shift lock loop follows correctly the frequency of the input signal.