Performance of Hydrogen Maser and Its Usage in Local atomic time at NTSC

The advantage of a hydrogen maser is in its short-term stability, however, with the same hydrogen masers, their performance are different. In 2004, four hydrogen masers were bought to time keeping laboratory of NTSC, two of which were made in USA, and the other two in China. In order to make full use of the hydrogen masers, it is necessary to study their performance which includes the short-term stability, long-term stability, noise, frequency drift etc. Through the exhaustive study and analysis one could exactly know their different performances, and consequently different methods could be studied when they participate in the calculation of local atomic time (TA). In this paper, the performances of the four hydrogen masers are discussed with the emphasis on the two hydrogen masers made in America, by analyzing the data which are obtained from the time comparison system at NTSC, and then the method of how to use them in the calculation of TA(NTSC) is studied. By using the method, the short-term stability of TA(NTSC) increases obviously.