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用接收机接收信号时,如果信号的强度不是在一定程度以上的话,那末,无论什么样的信息送来都不能判定,这是因为有噪声的存在。噪声大致区分为外界噪声和内部噪声两种。外界噪声是在外部产生进入接收机输入端的噪声,它包含了人工噪声及宇宙噪声等,外界噪声即便在接收机上下功夫,也是不能将其消除的。内部噪声是在接收机内部产生的噪声,它使信噪比变坏,是影响接收机性能的主要因素。
Receiving signals with the receiver, if the signal strength is not above a certain level, then, no matter what kind of information can not be sent, it is because of the presence of noise. Noise is roughly divided into two kinds of external noise and internal noise. External noise is generated outside the receiver input noise, which contains artificial noise and cosmic noise, the external noise even if the receiver work hard, but also can not be eliminated. Internal noise is the noise generated inside the receiver, which deteriorates the signal-to-noise ratio and is a major factor affecting receiver performance.