ELECTRONIC TUNER

PURPOSE:To obtain high educational FM jamming excluding ability without degrading respective characteristics in the case of reception at another channel by switching the bias setting of a mixer circuit while responding to an FM trap switch signal in the case of reception at a specified channel. CONSTITUTION:Since the FM trap switch signal at an H level (+B) is applied to the mixer circuit in the case of reception at the specified channel (6 channel), a base voltage Vb of a mixer transistor(Tr) becomes an expression I. On the other hand, since the FM trap switch signal at an L level 0V is applied in the case of reception excepting for the 6 channel, the base voltage Vb of the Tr becomes an expression II. Thus, various voltages are biased to the base according to the ON/OFF of the FM trap signal, namely, according to whether the reception is executed at the 6 channel or the other channel. This bias voltage is set to be optimize third-order distortion for excluding educational FM jamming, and set so as not to degrade the respective characteristics while regarding important converting gain and secondary distortion or the like in the case of reception excepting for the 6 channel.