LI Yu-ying1, 2, LIU Tie-xin1, CHEN Wen-xing1, XIE Yong-hui1

(1. Shanghai Astronomical Observatory, Chinese Academy of Science, Shanghai 200030, China;

2. Graduate University of Chinese Academy of Science, Beijing 100039, China)

Abstract: The long-term frequency stability is an important indicator to a passive hydrogen maser. In order to improve the long-term frequency stability an experiment is designed to analyze the impacts of hydrogen atom flow changes on the output signal frequency for different cavity frequency. The experiments show that the impact of flow change on the frequency stability will be minimal when the cavity frequency control voltage is locked at tuning point. However how to lock the microwave cavity to tuning point and how to minimize the flow change need to be explored to improve the long-term frequency stability for single frequency modulation.

Key words: passive hydrogen maser; flow change; long-term frequency stability