Correlation measurement of co-located hydrogen masers

Abstract

The correlation of co-located hydrogen masers (H-masers) is difficult to measure because their common-mode noise induced by the environment will be cancelled out during the comparison measurement. With the development of fibre-based high-precision time and frequency transfer techniques, the correlation of co-located hydrogen masers can be directly measured with the help of remote H-masers. Recently, a fibre-based frequency synchronization network was constructed in the Beijing region by connecting five H-masers from four institutions. The correlation coefficient of atomic clocks is defined and the correlation between two co-located H-masers is measured using both experimental and simulative methods. The results show that the correlation is not prominent until the averaging time is larger than ∼103 s; then, the coefficient grows rapidly for average times ranging from ∼103 s to ∼105 s and decreases beyond ∼105 s up to 5 d.