Pictured above is a series of images digitally stacked so that all of the stars images coincide. Here, Mars appears to trace out a loop in the sky.

上面图是一系列数码照片叠加而成的，让恒星重合，而火星貌似在天空中画了一个环。

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The design of code loop is the key point in the ranging system. And the choice of its parameter greatly affect the trace curve.

码跟踪环的设计是伪码测距系统的一个关键环节，其参数的选择对环路跟踪曲线影响很大。

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The phase- locked loop is one kind of control system which is able to achieve phase automatic lock, to compose frequency and to trace demodulation system.

锁相环路是一种能实现相位自动锁定的控制系统，主要用于频率合成及跟踪解调系统。

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