Abstract: In order to overcome the shortcomings of the traditional experiment box of the communication principle in signal processing and detection, it is necessary to use simulation to show the experimental phenomena in a more comprehensive way. However, Simulink, LabVIEW, and other software can only simulate the digital communication system. To solve this problem, Multisim is used to perform component-level circuit simulation of analog communication systems, including PAM ( Pulse Amplitude Modulation) encoding and decoding, FSK (Frequency Shift Keying ) modulation and demodulation, and PSK ( Phase Shift Keying ) modulation and demodulation. Through simulation, the inherent working mechanisms of sampling theorem, phase-locked loop, and Costas loop are intuitively demonstrated, and the principles of two possible distortions that can occur during FSK demodulation are thoroughly analyzed. 

Key words: communication principle experiment, Multisim simulation, pulse amplitude modulation, frequency shift keying, phase shift keying