中文说明：AFC自动频率控制是用来消除频率偏差的。自动频率控制环是一种带反馈的误差闭环控制系统，其中共轭相乘是通过鉴频算法，提供频率估计的误差值，以调整载波NCO，达到频率跟踪的目的。
English Description：
AFC automatic frequency control is used to eliminate frequency deviation. Automatic frequency control loop is an error closed-loop control system with feedback. Conjugate multiplication provides the error value of frequency estimation through frequency discrimination algorithm to adjust carrier NCO and achieve the purpose of frequency tracking.