Satellite VHF transponder time synchronization

Abstract

This paper describes an experiment designed to transfer ments have been conducted [I], [2] previously using satelaccurate time between two widely separated clocks using a VHF satellite Satellite, ATS-1. The experiment used atomic oscillators to maintain accurate time at each station, and the synchronization was accomplished by measuring the round-trip delay times between the stations. The goal of the experiment was to evaluate a V H F system, because of the low-cost ground equipment involved, in contrast to microwave systems. The paper discusses the results and the various factors that contributed to the timing errors. lites with microwave transponders. The present experiment transP'"'der* The &elbte used was the NASA Applications T=h""l"gy was conducted with the ATS-1 VHF transponder. Although the microwave frequency region is ideal from the point of system has an advantage in that relatively simple and lowclocks was achieved to within a few microseconds. view of avoiding atmospheric signal distortion, the VHF cost ground equipment may be used. Synchronization ofthe Manuscript

Worldwide Clock Synchronization Using a Synchronous Satellite

“…2 ) Mode I I Accuracy: The accuracy associated with the Mode I1 technique (using the equipment and pro-cedures of this experiment), has been shown to be about 5 ps [ 3 ] . T h e least accurate Mode I1 synchronizations during this experiment were between Stations N and V (average values were 7.7 and 8.8 p s ) .…”

“…T h e accuracy of measurement was f 1.0 p s [9]. c) T h e locations of the stations were known to within 200 meters corresponding to a propagation time uncertainty of fO.5 p s [from (3)].…”

“…This method, which has been used and reported on before [3], was used in support of the Mode I experiment to check the time differences between the station clocks. T h e locations and ranges of the master and slave clocks need not be known, but both master and slave stations must have transmitters.…”

WWVB

“…Satellite signals could cover large areas of the Earth with very little power, and the signal paths were exceptionally stable. NBS had already begun time synchronization experiments via satellite at the time of Milton’s report [ 52 ].…”

The GOES time code service, 1974-2004: A retrospective

“…Time synchronization experiments using VHF (135.6 MHz downlink) transmissions from the NASA Application Technology Satellite (ATS-1) were conducted in 1967. These measurements compared clocks located in Colorado, Hawaii, and California by making round trip time delay measurements via the satellite transponder, resulting in time synchronization uncertainties of just a few microseconds over a 10 d period [ 15 ].…”