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在收音机的放大电路中,由于存在不应有的正反馈而引起的振荡现象,称为“寄生振荡”或“自激振荡”。中频产生的自激振荡,它的振荡频率会与变频级输出的中频信号产生差拍,从而出现啸叫,影响正常收音。 产生中频自激振荡的原因有:(1)由于中放管集电极-基极的极间电容C_C的作用,使中放级产生内部反馈;(2)由于杂散电容使中放级的输出与输入电路产生有害的耦合;(3)由于电池内阻较大,各级电流通过这一电阻产生足够的反馈;(4)中放管的β值太高。 针对以上原因,可采取以下相应措施消除自激振荡:
In the amplifying circuit of the radio, the phenomenon of oscillation due to the undue positive feedback is called “parasitic oscillation” or “self-oscillation.” IF self-excited oscillation, its oscillation frequency with the frequency level output of the intermediate frequency signal beat, resulting in howling, affecting the normal radio. Intermediate frequency self-oscillation causes: (1) due to the collector tube - the base of the polar capacitor C_C role in the intermediate release level to produce internal feedback; (2) due to stray capacitance so that the output level And the input circuit harmful coupling; (3) due to the larger battery resistance, all levels of current through this resistance to produce sufficient feedback; (4) in the tube of the beta value is too high. For the above reasons, the following measures can be taken to eliminate self-oscillation: