Royal Observatory of Belgium Clocks and Time scales:

clocks HP5071A with standard tubes, one active H-maser CH1-75 and one passive H-maser CH1-76. A new H-maser CH1-75A has been installed in December 2005, it should replace the CH1-75 for the generation of UTC in the coming months, when it will have reached a sufficient long-term stability. The time laboratory temperature variations are kept smaller than 0.2°C. During the period 2004-2006, the UTC(ORB) time scale was generated from the frequency of the H-maser CH1-75, of which the auto-tuning is based on the 5Mhz frequency from the passive H-maser CH1-76. The monitoring of UTC(ORB) is performed daily from a comparison with the USNO Master Clock MC3 used to steer the USNO Ashtech Z-XII3T receiver (IGS station). This comparison is done using the self-developed RINEX-CGGTTS conversion software using the P3 ionosphere-free combination and IGS rapid and ultra-rapid orbits. The behavior of UTC(ORB) with respect to UTC is shown in Figure1. The epochs of large variations correspond to maintenance of one of the masers due to failures; at these epochs UTC(ORB) was realized by a cesium clock. The ROB also installed a redundant NTP system for distribution of UTC(ORB) via the internet