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5.1 引言 VTR采用了相干的AGC,以便当进入跟踪装置的第一混频器的信号电平高于-85dBm时,使进入载波和测距环路的鉴相器的信号电平尽可能保持接近不变,如图5.1所示。当输入信号超过-85dBm及AGC正常工作以后,在有增益控制的中频放大器后面的限幅器起线性放大器的作用。因在这些信号电平内无限幅,故AGC引起的任何噪声都会加到鉴相器去。本文的目的,是对这种噪声影响进行估算。
5.1 Introduction The VTR employs a coherent AGC so that the signal level of the phase detector entering the carrier and ranging loop remains as close as possible when the signal level of the first mixer entering the tracking device is above -85 dBm Unchanged, as shown in Figure 5.1. When the input signal exceeds -85dBm and the AGC is working properly, the limiter behind the gain-controlled IF amplifier acts as a linear amplifier. Due to the unlimited amplitude of these signals, any noise caused by the AGC is added to the phase detector. The purpose of this article is to estimate the effect of this noise.