This document summarizes research analyzing the stability of GPS oscillators within Serbia's permanent GPS station network. The researchers analyzed data from 30 stations to calculate Allan variance and power spectral density graphs. They found that most stations exhibited flicker frequency modulation noise processes, but some showed different characteristics likely due to environmental factors. Older receiver models generally had higher Allan variances. The results indicated only flicker frequency modulation and random walk frequency modulation noise processes. Calibration of GPS receivers was determined to be important for ensuring accuracy.