Validation of the inter-frequency calibration of timing GNSS receivers

This paper presents a study of the consistency of the values used as reference for the hardware delays of GPS P1 and P2 for calibration in the TAI network. The inter-signal biases dP1-dP2 are computed from the pseudorange measurements, after applying an ionospheric delay correction, and then compared to the calibrated values. It is shown that the differences between the computed dP1-dP2 and the calibrated values are well inside the expected combined uncertainty. A similar conclusion is reached comparing the computed dP1-dP2 with absolutely calibrated stations. We also show that using a same antenna phase center for the calibration or using different positions for L1 and L2 signals gives maximum differences of 200 ps on the hardware delays of the separate codes P1 and P2, but the final impact on the P3 combination is less than 10 ps. The computed dP1-dP2 are then also used to look at the stability of the inter-signal hardware delays of some GPS stations dedicated to time transfer. It is shown that only variations larger than 2 ns can be detected in the computed dP1-dP2 for a particular station, while variations of 200 ps can be detected when differentiating the results between two stations.