Print WANG Zheng-ming
（National Time Service Center, Chinese Academy of Sciences, Xi’an, Shaanxi 710600, China）
Abstract：The requirement for automatically monitoring and controlling the BPL working clock signal T（PU）has been requested by the renovation project of the Long Wave Time and Frequency Broadcasting System （BPL）at National Time Service Center（NTSC）, the Chinese Academy of Sciences. The specifications for the T（PU）controlling must achieve the absolute phase time difference,︱UTC（NTSC）- T（PU）︱ , smaller than 50 ns, where UTC（NTSC）is the master clock signal generated by the Standard Time and Frequency Laboratory of NTSC and the absolute frequency offset of T（PU）< 5.0×10-13. In order to reach the specifications and improve T（PU）as accurate as possible , the methods for monitoring and controlling T（PU）are discussed for several different kind of atomic clocks, which are used as the frequency sources of the working clock. As a result, for the atomic clocks with better short term（τ～1 d）frequency stability, which is used as the frequency source of the working clock，the quasi-real time predicted frequency and the measured phase offset between UTC（NTSC） and T（PU）can be used to calculate the frequency compensation that should be set on the micro-phase stepper to realize the working clock frequency steering, so as to greatly improve the accuracy of T（PU）. For the atomic clocks, used as frequency sources, with worse short term frequency stability, the quasi-real time predicted frequency is far from accurate as needed, so the averaged frequency offset of a few months as well as the real time measured phase time difference can be used for the frequency steering in order to meet the controlling specification.
Key words：working clock signal；frequency steering；phase compensation；accuracy；frequency stability