An NBS calibration procedure for providing time and frequency at a remote site by weighting and smoothing of GPS common view data

The National Bureau of Standards (NBS) Time and Frequency Division now performs precision time and frequency transfer using common view measurements of Global Positioning System (GPS) satellites as a calibration service. Using this service, we have been able to transfer time with time stabilities of a few nanoseconds, time accuracies of the order of 10 ns, and frequency stabilities of one part in 10
¹⁴
, or better, for measurement times of about four days and longer. The full accuracy of the NBS primary frequency standard is now available at a remote site. This paper describes the technique used for weighting and smoothing the data to produce these levels of stability and accuracy. All of the primary frequency standards used in the generation of International Atomic Time (TAI) now use this technique.