The electronic improvement of the hydrogen maser for time keeping application

The hydrogen maser for time keeping must have excellent performances with long term frequency stability, low frequency drift and high reliability for long term working. Based on the research experiences on hydrogen masers of Shanghai Observatory, the key technical improvements for time keeping hydrogen masers are described in this paper. The mainly electronic improvements include: analysis on the principle of the cavity auto-tuning technique and improving the modulation system, the development of phase-lock receiver. The primary test result reaches the expert performance as follows: the frequency stability reaches 1.5E-15/day, frequency drift rate is 8.6E-16/day, and temperature sensitivity is 8.1E-15/°C.