Results of the 2008 TWSTFT calibration of seven european stations

In 2008, seven European institutes participated in a TWSTFT calibration campaign to determine the internal signal delays of their ground stations relative to the portable reference station of Joanneum Research, Graz. In a second step, the calibration values and their uncertainties for time comparisons of 21 links involving the participating institutes were determined. The following results were obtained. The common clock differences between the two TUG stations measured in October 2007, August 2008 and October 2008, respectively, agreed within 0.5 ns, proving the suitability of the traveling station as a reliable and stable traveling reference. After substantial changes in the hardware, the links connecting to NPL and VSL were calibrated with uncertainties slightly exceeding 1 ns and 2 ns, respectively. The so-called TAI links OP-PTB, INRIM-PTB, and METAS-PTB were recalibrated. Despite hardware changes and a change of the satellite in use in early 2008, the calibration values measured this time agreed with the values determined in 2005 and 2006 well within the calibration uncertainty of slightly above 1 ns.