Research on modification of H-maser drift

The atomic H-masers are widely used in time keeping nowadays. BIPM has changed clock frequency prediction method since September 2011 based on weighting the clocks according to their predictability. An H-maser characterized by a very significant frequency drift can be used in time keeping because its behavior can be well predicted. The clock ensemble of UTC(NIM) consists 6 H-masers (5 at the new campus) and 7 Cs clocks, an H-maser is chosen as the master clock. All the H-masers are model MHM-2010 made by Symmetricom. In order to verify whether the frequency drift of H-masers can be modified manually, some tests were performed and the results showed that the frequency drift of the MHM-2010 H-maser could be somehow modified by changing its Hydrogen pressure. The test procedure and the results are introduced in this paper.