reportonthe timeand frequency activitiesofthe time（reportonthe时间和频率activitiesofthe时间）.doc

Time For LORAN Demetrios Matsakis and Harold Chadsey Time Service Department U.S. Naval Observatory Washington, DC ABSTRACT No one can stop time, but time can stop a system. Users need to be aware of the different flavors of time, depending upon their needs. Most systems require that all their components be on a common time (synchrony), but they cant keep them on time unless they are also on a common frequency (syntony). Other systems simply require syntony. All systems should have a backup. The U. S. Naval Observatory (USNO) is the timing reference for LORAN and GPS. Its Master Clock (MC) is based upon 72 HP5071 cesium and 18 hydrogen maser frequency standards in three buildings at two sites, and their data are used to generate UTC(USNO). The USNO disseminates time via LORAN, Network Time Protocol (NTP), GPS and Two-Way-Satellite Time Transfer (TWSTT). Our emphasis is on robustness through repeated calibration and multiplicity of systems, and we recommend this for our users as well. Further details and explanations of our services can be found on , or by contacting the author directly. I. Raw Time The most important part of the USNO Time Service Department is its staff, which currently consists of 26 employees. Of these, the largest group, about half the staff, is directly involved in time transfer. The rest are fairly evenly divided between those who service the clocks, those who monitor them, and those who are trying to develop new ones. The core stability of USNO time is based upon our clock ensemble. We currently have 72 HP5071 cesium clocks and 18 cavity-tuned “Sigma-Tau/Datum” hydrogen maser clocks, which are located in two Washington, D.C. buildings and also at the USNO Alternate Master Clock (AMC), located at Schriever Air Force Base in Colorado. The clocks used for the USNO timescale are kept in 19 environmental chambers, whose temperatures are kept constant to within 0.1 degree C and whose relative humidities (for all masers and m