Progress in the link calibration for UTC time transfer

The dominant part of the total uncertainty budget in the [UTC-UTC(k)] is from the type B uncertainty (u
_B
) in time link calibration. In fact, 60% of the type A uncertainty (ua) in UTC time links are <; 1 ns while the 93% of u
_B
≥ 5ns. In 2011, the BIPM launched a pilot experiment to reduce the u
_B
from 5 ns at present to ≤ 2 ns and has developed a standard calibration scheme, namely METODE, associated with an integrated portable GNSS calibrator together with the reference receivers stationary at BIPM. Similar setups are made in TL. Using these systems, we performed a series experiments at BIPM, OP and TL to study the attainable uncertainty of METODE. The results are compared to that of the traditional differential receiver calibrations.