Long term study of the H-maser clocks at the Royal Observatory of Belgium

Two hydrogen masers are in operation in the time lab of the Royal Observatory of Belgium. One is a CH1-75 operational since 1991 and the other one is a CH1-76 operational since the 1999. This second one is used to provide a frequency needed by the active HM CH1-75 for the cavity auto-tuning. The stability of the masers since their putting in operation is studied.