Abstract: This paper discusses a highly stable X-band local signal source developed for recent years, which can be used for noncoherent MT1 and MTD radar. The source consists of a microwave phase-locked loop and a new type of automatic frequency control circuit. Chief factors to influence spectrum purity of microwave output signal and phase noise are analyzed. The paper also discusses a kind of frequency-voltage single value response's discriminator that is made up of low-pass filter and a kind of digital-analog combining automatic frequency control circuit. The local signal source has operated properly not only in stabilizing frequency of the PLL mode, but also in tracking of transmiter frequency drift. Main characters and experimental results are given.