说明：   DSB-AM方式，进行信号的调制和解调 输出1：已调信号的波形 输出2：消息信号和已调信号的频谱 输出3，恢复信号的波形
( DSB-AM mode, the output signal modulation and demodulation 1: of the output waveform of the modulated signal: the message signal and the spectrum of the modulated signal output 3, restore signal waveform)