Positioning of GPS antennas in time-keeping laboratories of North America

The problems with the use of the Global Positioning System (GPS) for time transfer are discussed. The Bureau International des Poids et Mesures (International Bureau of Weights and Mesures, BIPM) has developed a method of differential positioning using the data of time comparisons themselves. The consistency of the coordinates is within 30 cm for distances up to 1000 km. The method was applied to the European laboratories one year ago (1988). The consistency of time comparison improved from about 10 ns to about 2 ns. The principles of this technique and the results of its application to the North American time laboratories are presented. Work on differential positioning by geodetic double-frequency receivers between the US Naval Observatory and the Maryland VLBI (very long baseline interferometry) point are reported.<<ETX>>