To prevent deterioration of the receiving S/N and the data error rate by inserting a variable attenuator between an RF input part and a front end to control the attenuation of an attenuator in response to the receiving input level.
The receiving signal inputted from an RF input part is converted into the intermediate frequency through a variable attenuator 7, a front end 8 and a 1st mixer 9. The converted receiving signal is converted again into the 2nd intermediate frequency through an intermediate frequency part 10 and a 2nd mixer 11. Then the signal of the 2nd intermediate frequency is demodulated and also inputted to a detector 5 to be turned into a DC voltage signal which is proportional to the receiving signal inputted to the RF input part. A control part 20 compares the digital value obtained by applying the A/D conversion 6 to the DC voltage of the detector 5 with the prescribed reference value and controls the attenuation of the attenuator 7 based on the comparison result.
AKIYOSHI KATSUHISA
OBAYASHI KATSUKI
