Two-way time transfers between National Research Council /Ottawa/ and Paris Observatory via the 'Symphonie' satellite

Time comparisons using the 4-6 GHz channels of a communication satellite between Canada and France were achieved on a routine basis. The precision between telecommunication terminals is of the order of 1 ns, but the accurate calibration of instrumental delays has not been solved; another problem is the transmission of time between telecommunication terminals and the standard laboratories, at distances of 10-500 km, with a matching precision. Recent experiments between the U.S. National Bureau of Standards, the U.S. Naval Observatory, the National Research Council of Canada, and the Center of Plemeur-Bodou (France) have shown that the simultaneous time comparisons using two satellites can extend the geographical coverage of the method; the system can be considered to provide a worldwide coverage with a relatively small number of ground stations and satellites.