The Technology and Research of Hydrogen Maser Modulation

For hydrogen atomic clock, the oscillation frequency of the cavity will be affected due to the cavity pulling effect of the microwave cavity and the temperature change of the external environment. This affection results in the decrease of the long-term stability of the hydrogen atomic clock. In order to correct this situation, we use cavity auto-tuning methods to stabilize the cavity frequency at service frequency. At present, main technology of auto-tuning of cavity consists of three kinds:external detection signal tuning mode, microwave cavity frequency switch tuning mode and Q_a modulation mode. In this paper, we analyze the tuning mode of external detection signal and microwave cavity frequency switch. In addition, we make further exploration of the microwave cavity frequency switch tuning method based on external detection signal tuning mode of Shanghai Astronomical Observatory SOHM-4 hydrogen atomic clock. We make circuit design and program development on digital signal processor. Consequently, cavity auto-tuning method is implemented on SOHM-4 hydrogen atomic clock.