This article has made the improvement to CPAFC which be commonly used. After the improvement frequencydiscrimination algorithm has the quicker capture speed.
对常用的叉积自动频率跟踪环（CPAFC）进行了改进，改进后的鉴频算法具有更快的捕获速度。
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In this paper a distant image play-out system designed with the principle of frequencydiscrimination, main technical measures and main technical specifications are described.
Then the differential frequencydiscrimination method, especially at slow data rates, is discussed while a practical structures of differential frequencydiscrimination is given.