| 摘要 |
PURPOSE:To improve the overall reception sensitivity of a receiver while noise is reduced and crosstalk is suppressed by bringing the impedance viewed from the input side into an infinite value substantially at an intermediate frequency and short-circuiting the impedance to a frequency near DC. CONSTITUTION:A series circuit comprising an RF chock coil L2 and an IF choke coil L3 is inserted to the input impedance matching circuit 2 of an intermediate frequency IF amplification first stage transistor (TR) 3 so as to short- circuit the input impedance of the matching circuit 2 with respect to the frequency near DC in an intermediate frequency conversion section with respect to a local oscillation frequency and a radio frequency RF inputted via a band pass filter 1. The noise figure is improved by short-circuiting the input impedance to the 1st mixer TR at a DC or the frequency near the DC.
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