Investigating the correlation between hydrogen-maser clocks in the same place

Using fiber based frequency dissemination system, we are building Beijing regional time and frequency network. Currently, Tsinghua University (THU), the Changping site of National Institute of Metrology (NIM-Changping) and Beijing Institute of Radio Measurement (BIRM) have been linked and synchronized via the fiber network. The frequency signals of three hydrogen masers, two placed in NIM, one in BRIM are transferred to Tsinghua University, and compared with the local hydrogen maser. By this remote comparison, the absolute frequency stability of each clock as well as the correlations between the two clocks in NIM are measured and studied.