Double superheterodyne AM radio receiver

摘要

PURPOSE: To prevent the interference of the amplitude modulation waves of other radio stations within the same band by arranging a switching circuit for forming an LPF or a high frequency tuning circuit between a high frequency amplifier circuit and a first frequency converter part. ;CONSTITUTION: The plural amplitude modulation waves fetched by an antenna 1 are passed in asynchronism through the FET 2 of the high frequency amplifier circuit and supplied to the switching circuit 13 and the output is inputted to a first frequency mixer 4. In the switching circuit 13, in the case of receiving the amplitude modulation waves of a medium wave band, a current is supplied to the base of a transistor Q1 and the base of a Q3 through a terminal 23 and the current supplied to the base of a Q2 is interrupted. Thus, the circuit 13 becomes the high frequency tuning circuit for which a coil L2 and a variable capacitive diode D1 are parallelly connected. Further, in the case of receiving the amplitude modulation waves of a long wave band, the circuit 13 displays the function of the LPF.;COPYRIGHT: (C)1996,JPO