A phase-coherent link via synchronous satellite developed for very long baseline radio interferometry

A high-precision, phase coherent link between remote interferometer stations has been developed and has been utilized in a transcontinental radio interferometer to assess the feasibility of improved astrometric and geodetic measurements. A dual-tone transmission method effectively cancels most phase-degrading effects. An experimental Allen variance curve indicates that stability of 1 × 10^-13 was achieved over a 1-hour period; the slope of the Allen variance curve was close to - 1 for all time intervals up to 24 hours, indicating that the link is truly phase stable at frequencies of less than 1 GHz. Changes in the link path were measured with an accuracy of 300 ps, corresponding to 10 cm, over periods of several hours.