中文摘要：

为提高系统的长期频率稳定度（它是被动型氢钟的一个重要指标），设计了一种实验，用以分析在不同微波腔谐振频率下，氢气流量变化对输出频率的影响。通过实验发现微波腔的控制电压存在一个调谐点，在调谐点附近，流量变化对输出频率的影响变小。但是对于单频系统，如何将微波腔锁定在调谐点附近以及如何减小流量的影响和提高系统的长期频率稳定度还需要进一步探索。

英文摘要：

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.