Abstract: This paper presents a phase locked loop oscillator based on an LMX2306 chip of the National Semiconductor.The oscillator has many merits, such as convienience in assembling, real-time computer controlability, low-level power consumption, long-time operational stability, and flexibility in programming.The oscillator has been used in the receiver of the demonstrative model of the FAST as a local oscillator for the second down converter.Its performance has been proved by observational experiments with the demonstrative model.