Inter-comparison of the UTC time transfer links

We present the new side-product of the monthly UTC computation: the long-term time links which is monthly published since Jan. 2010 and available on the BIPM ftp site: ftp://tai.bipm.org/TimeLink/LkC/LongTerm/. The techniques used for UTC generation are now TW, GPS and GLN. If they are considered independent, we can apply them in the investigations of the measurement uncertainties and the relative long-term variation in the link calibrations. 26 months' data have been collected and analyzed in this paper. For the short term measurement instability, we have similar conclusion as presently given in the section 6 of the BIPM Circular T. It seems however, for some baselines, exist long-term variations in the link calibrations. Limited by the knowledge of the raw data, we cannot explain the causes of this instability. Except for the extreme cases, most of the annual variations are within 2 ns. This is the limit of the uncertainty of the nowadays instrumentation and calibration and should not affect the UTC generations beyond its total uncertainty.