Time from European time keeping laboratories via telephone modem

The time keeping laboratories of Austria, Germany, Italy, Netherlands, Portugal, Sweden, United Kingdom offer telephone time services which allow a computer to receive traceable time information from the national time standards by direct telephone line. The coded time information is sent using a common format, the "European Telephone Code". Far users requiring high accuracy the uncertainty with which the time information can be received is of particular interest. Most of the time code generators established for this service in Europe have been developed at the Technical University of Graz (TUG) and provide the feature to measure the round-loop delay in a two-way mode and to correct for the one-way delay. Propagation delays of various telephone connections have been studied. The arrival times of the telephone time signals from the PTB, the TUG and the VSL (Van Swinden Laboratory in Delft) have been measured in the one-way and the two-way mode at the PTB in Braunschweig and the FTZ in Darmstadt. The results show that uncertainties of a few milliseconds are achievable with this technique.