Design of a Communication Demodulation Experimental System with Carrier Tracking Function

In current high-frequency circuit experimental teaching, there is a lack of reported experimental content related to Automatic Frequency Control (AFC). A communication demodulation experimental system is designed with carrier tracking capability. The system employs a feedback mechanism to extract the carrier center frequency drift of input signals in real-time, controls the Voltage-Controlled Oscillator (VCO) to dynamically adjust the local oscillator frequency, thereby achieving real-time tracking and demodulation of frequency-modulated signals with dynamically drifting carrier center frequencies. Experimental results demonstrate that the system can achieve a maximum carrier frequency tracking range from 33.2 to 38.1 MHz. When the carrier center frequency drifts following sinusoidal, triangular, or square wave patterns, the maximum tracking frequency approaches 100 Hz, with demodulated waveforms exhibiting high signal-to-noise ratio, stability, and nearly distortion-free characteristics. The experimental system validates relevant theories of AFC loops in communication circuits and provides a practical solution for carrier tracking and demodulation in complex electromagnetic environments such as communication systems and satellite navigation.