求翻译：根据（6-14）式，得双极性归零码的功率谱的函数图形如图6-19所示。由此可知，从双极性归零码的功率谱的结果来看，不包含直流分量，但无码元同步信号分量。是什么意思？

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According to (6-14) type, results in the bipolarity nulling operation code power spectrum function graph as shown in Figure 6-19.Thus it may be known, looked from the bipolarity nulling operation code power spectrum result that, does not contain the direct component, but non-element synchronized sig

According to (6-14), bipolar return-to-zero code power spectral density function graph as shown in Figure 6-19. It can be seen, from the power spectrum of bipolar return-to-zero code results, does not contain a DC component, but $ wuma synchronous signal components.

According to (6-14) type, must pairs of polarity return zero yard of function figure of power spectrum show as in Fig. 6-19. Know from this, return from pairs of polarity zero yard of result of power spectrum watch, include the direct-flow weight, but there is no synchronous signal weight of yuan of