Doppelmodus-Zellulartelefonsystem

摘要

The present invention is directed to provide a dual-mode cellular telephone system which is capable of suppressing a narrow-band disturbing signal appearing in a mobile station of a dual-mode cellular telephone system adapted to an analog system and digital CDMA system. A CDMA signal from a CDMA base station and a narrow-band signal from an analog system are received through an antenna (101) by receiver (102) whereby they are amplified, subjected to frequency conversion and, then, input to a variable notch filter (105). A disturbing signal detection circuit (106) supplies the variable notch filter (105) with a control signal for making its frequency be variable. Namely, the disturbing signal detection circuit (106) detects a case that an output level of the variable notch filter (105) becomes minimal by changing the notch frequency by sweeping control signals. A control signal at which the output level of the variable notch filter (105) is minimal is fed to the variable notch filter (105).