Research activities on time and frequency transfer using space links

Time and Frequency (T/F) transfer systems using space links developed at the Radio Research Laboratories (RRL) are described. The domestic T/F transfer system uses the Japanese communication satellite: CS-2/broadcasting satellite BS-2 and the Global Positioning System (GPS) in addition to the ordinary links of ground TV and Loran-C The Asian area transfer system makes use of the Geostationary Meteorological Satellite (GMS) and a Very Long Baseline Interferometer (VLBI) as well as Loran-C Other systems for international T/F transfers depend on the space techniques of the GPS and the, VLBI. Spread-spectrum equipments for T/F transfers have recently been built to realize both precision and accuracy of about 1 ns via the CS link, together with a 1-m mobile antenna station. Receivers have been developed at RRL to be used routinely for the GPS and GMS T/F transfers on a daily basis with a precision of 10 ns or more and an accuracy of less than 100 ns. T/F transfer experiments using a VLBI system developed at RRL have been conducted on a routine basis about once a month with the U.S. Naval Observatory since April of 1985. The present goal of accuracy is 10 ns with 10-min or longer observations.