Calibration of dual frequency GPS receivers for TAI

Dual-frequency P-code GPS receivers have been used for time comparisons for several years. They are now standard equipment with units in operation in some 25 time laboratories contributing to TAI. Calibration of these receivers is necessary to ensure the accuracy and long-term stability of time links used in the computation of TAI. A few years ago, only one model of dual-frequency receiver was commercially available and the calibration effort was focused on this receiver. Presently, several different models of receivers are available and used in time laboratories. The paper presents inter-comparison methods and calibration procedures for these three types of receivers, along with some results of differential calibrations. The list of such receivers is due to expand as new models are being introduced. Disclaimer: Some commercial equipment are identified in this paper in order to describe the experimental procedure adequately. It does not imply recommendation or endorsement by the authors or their institutions.