一、概述近年来,短波频段使用的日趋拥挤,发射功率的日益增高,使接收机往往不得不处在与信号频率相距极近的强干扰条件下进行工作.这些干扰频率虽处在接收机通频带之外,但因前几级电子管受强干扰作用而处于非线性状态下工作,往往会引起信号阻塞、交叉调制等附加干扰.短波干线通信的距离极长,加上短波传播中经常有的衰落现象等,这就确定了短波干线通信接收机必须是高灵敏度的,显然,这种高灵敏度接收机是更容易 I. Overview In recent years, the use of shortwave frequency band is becoming increasingly crowded and the transmission power is increasing day by day, so that the receiver often has to work in the strong interference condition which is very close to the signal frequency. Although these interference frequencies are in the receiver Frequency band, but because of the first few levels of strong interference by the role of the tube in a non-linear state of work, often lead to signal blocking, cross-modulation and other additional interference. Short-wave trunk communication distance is extremely long, coupled with the short-wave propagation often Fading phenomenon, etc. This confirms that the HF communication receiver must be highly sensitive. Obviously, this highly sensitive receiver is easier