用matlab实现的曼彻斯特编码。50 占空比（可调）。绘制时域波形和频域功率谱密度。结果跟北邮的郭文斌的通信原理课件上的形状一模一样。-Manchester encoding with a matlab implementation. 50　duty cycle (adjustable). Draw time-domain waveform and frequency domain power spectral density. The results with the Beijing University of Posts and Telecommunications of the GUO of communication theory on the shape of the same courseware.