题目内容

Compare the capability of high-frequency signals and low-frequency signals in straight-line propagation, reflection, refraction, and diffraction.比较高频信号和低频信号分别在直线传播、反射、折射和衍射的功能？Answer:Low-frequency signals can travel around the lower part of the atmosphere by ground propagation. They can travel with diffraction, refraction, reflection, or straight-line propagation.Higher-frequency signals can travel up to the ionosphere and reflect down to the earth by sky propagation. Most of them can also travel with refraction, diffraction, reflection, and straight-line propagation.Very high-frequency signals which are very unidirectional are transmitted from the source to the destination directly only by straight-line propagation.

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1. Among unipolar NRZ-L, Polar NRZ-L, NRZ-I, and RZ, Manchester, differential Manchester, AMI, and MLT-3, which schemes have no issues on synchronization, baseline wandering, and DC components, respectively?Answer:With self-synchronization problem: unipolar NRZ-L, polar NRZ-L, polar NRZ-I, AMI, MLT-3With baseline problem: unipolar NRZ-L, polar NRZ-L, polar NRZ-IWith DC components problem: unipolar NRZ-L, polar NRZ-L, polar NRZ-IWithout self-synchronization problem: polar RZ, Manchester, differential ManchesterWithout baseline wandering problem: Manchester, differential ManchesterWithout or with very little DC components problem: polar RZ, Manchester, differential Manchester, AMI

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