Long-Term Accuracy of Time Comparisons via TV Signal along Radio Relay Links

A time comparison method, which is based on TV synchronization pulses sent along radio links, was proposed and successfully tested in Czechoslovakia in 1967. Experiments performed afterwards in Europe and the U. S. confirmed the significance of this method. The instability of the overall propagation time delay along the radio links (including the equipment) is the major source of errors for long-term timekeeping between remote laboratories. In 1969, a research project on this subject was initiated in Italy, using the comparison of simultaneous time measurements by the TV method and integrated phase measurements via a coaxial cable between two remote laboratories that were located in Rome and Turin, Italy. The results show that the discrepancy between the TV results and the direct comparison by cable, over periods of 100 days, is usually less than 3 ¿s.