Traceability in atomic frequency standards

HP Santa Clara, the West Coast reference station for the US Naval Observatory, is described. Daily comparison of time between HP and UTC (USNO) are made using common-view GPS (Global Positioning System) techniques. The data obtained permit continuous tracking of a bank of cesium standards. The bank of standards is used internally as a house reference standard. The production area is located several hundred meters from the house standard. In the production area, an active "real-time" ensemble composed of three of the new HP5071A primary frequency standards is used as a local reference. Continuous measurement of the house standard and up to 31 units under test is made relative to the local reference. This permits easy determination of the relative difference between UTC and the standards under test. Each of the elements in the measurement chain between the GPS reference receiver and the frequency standard units under test is discussed