Time and frequency activities at the U.S. Naval Observatory

The U.S. Naval Observatory (USNO) has provided timing for the Navy since 1830 and, in cooperation with other institutions, has also provided timing for the United States and the international community. Its Master Clock (MC) is the source of UTC (USNO), USNO's realization of Coordinated Universal Time (UTC), which has stayed within 5 ns rms of UTC since 1999 and within 3.1 ns rms in 2008. The data used to generate UTC (USNO) are based upon 70 cesium and 24 hydrogen maser frequency standards in four buildings at two sites. USNO disseminates time via voice, telephone modem, LORAN, Network Time Protocol (NTP), GPS, and Two-Way Satellite Time Transfer (TWSTT). This paper describes some of the changes being made to meet the future needs for precision, accuracy, and robustness. Further details and explanations of our services can be found online at http://tycho.usno.navy.mil, which will shortly be transformed to http://www.usno.navy.mil.

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