| 摘要 |
PURPOSE:To obtain a sufficient image ratio with a simple circuit by using a high frequency as the 2nd IF by using a solid-state resonator for the 1st IF circuit of a double heterodyne AM receiver and selecting a high frequency as the 1st IF. CONSTITUTION:A double heterodyne system is applied to the all-band AM receiver and the difference between a received signal from an ANT input circuit 8 and the local oscillation signal of the 1st local oscillation 2 is led out of a transistor TR mixer 10 as the 1st IF. This 1st IF is applied to the base of the TR15 of the 1st IF amplifying stage through a capacitor 12. A bias resistance 14 and the solid-state resonator 13 are connected between the base and collector of the TR15 in parallel and a coil 16 with load impedance in connected to the collector. Then, negative feedback from the collector to the base is provided to minimize the impedance at the resonance frequency point of the resonator 13, to maximize the antiresonance frequency point, improving frequency characteristics of an amplifier. The difference between the 1st IF signal and a local oscillation signal from the 2nd local oscillation 5 is outputted from the 2nd mixing circuit 4 and a high frequency is used as the 2nd IF to obtain a sufficient image ratio. |
