h is a high frequency sound. High frequency is high frequency different from low frequency High frequency electronic circuit is an important technical basic course for electronics, information, communication and other majors, its basic task is to study the working principle of each unit circuit of the communication system, circuit analysis and basic design methods. The main contents of high frequency electronic circuit include: frequency selection network, interference and noise, high frequency small signal amplifier, high frequency power amplifier, sine wave oscillator, analog modulation and demodulation, feedback control system agc, afc, pll, frequency synthesis technology.