81st Annual Precise Time and Time Interval (PTTI) Meeting COMPARISONOFCOMMON-VIEWAND ONE-WAYGPSTIMETRANSFEROVERA 4000-KM EAST-WEST BASELINE

We have recently established a stable time scale in the Standards Laboratory at the Santa Clara site of Agilent Technologies to provide a reference for developing and testing GPS time-transfer products. The time scale consists of a high performance cesium frequency standard that is steered to follow UTC(lJSN0, MC) using the output of a commercial GPS-disciplined oscillator. The disciplined oscillator technique is subject to various errors, such as antenna position, broadcast ephemeris, propagation effects, local multipath, and inaccuracy in the GPS/UTC broadcast correction, as well as instrumentalfactors. The magnitude of these errors is often time-dependent, and not easy to predict. As a consequence of the long time constant used in the steering loop, the intrinsic frequency noise of the cesium standard is also significant. To provide an independent calibration, and to determine the overall accuracy of the time scale, we also carry out common-view time transfer with USN0 according to the BIPM schedule. It is well known that many time- transfer errors are considerably reduced by using the common-view technique. The common-view receiver system is portable, and has been calibrated by short baseline, common-clock operation at NIST. In the paper we will discuss the effects of various factors on the accuracy, stability, and traceability of the time scale. Data extending over about 185 days comparing the ‘common-view ’ and ‘one-way ’ time transfer methods will be discussed and compared with data from an independent system operating at Agilent Laboratories. We estimate the stability of the time scale to be about IO ns rms, and the traceability to UTC(USNO-MC) to be about IO ns at the I sigma level for measurements averaged over several days. Systematic differences between the one-way and common-view results will be discussed.