Background: In electronic LINAC

the magnetron is often used as power source.The output frequency of magnetron always changes with the environment and the frequency difference between the output of magnetron and the frequency of accelerator

which will result in the bad performance of LINAC systems.Purpose: To ensure the performance of the work of entire LINAC system effectively

an automatic frequency control system is necessary.Methods: A phase locked frequency discriminator is designed to discriminate the frequency of accelerator guide and magnetron

and analogue circuit is used to process the output signals of frequency discriminator unit.Results: Working with the automatic frequency control(AFC) system

the output frequency of magnetron can be controlled in the range of(2 998 MHz

2998 MHz+70 kHz) and(2 998 MHz

2 998 MHz-30 kHz).Conclusions: Under the measurement and debug

the functionality of frequency discriminator unit and signal processor circuit is tested effectively.