| 摘要 |
PURPOSE:To decrease noise at LW and MW bands by connecting a capacitor across a bar antenna, connecting the 1st stage to a common base cascade connection amplifier and the next stage to a common emitter cascade connection amplifier and applying feedback from the output stage to the input terminal. CONSTITUTION:A capacitor C 10 is connected across the bar antenna 1 and its resonance frequency is selected near the upper side reception frequency of the MW band. An output of the antenna 1 is connected to the emitter of a common base transistor (Tr) 2, the amplified output of the Tr 2 is connected to the base of the common emitter Tr 12, the negative feedback is applied from the collector of the Tr 12 to the input of the Tr 2 via a series circuit comprising a coil L 19 and a C 18 taking the resonance frequency as the lower reception frequency of the LW band or below so as to suppress the amplification factor for the reception frequency of the LW band lower side band. Further, the output of the Tr 12 is given to a bypass comprising a series circuit comprising a C 14 and an L 15 whose resonance frequency is selected to an intermediate frequency of the MW and LW bands so as to bypass an unnecessary reception frequency. Further, the value of the C 4 connecting the output of the antenna 1 to the base of the Tr 2 is selected to a value cutting off frequencies below the LW band lower side reception band. |
