COMSAT General Ranging Equipment Development

Abstract

The range to the spacecraft is an important parameter for determining the transfer and synchronous orbits. The ranging equipment developed for the COMSAT General TT&C earth stations uses a fixed-tone technique to determine the distance from the earth station antenna to the satellites. Specifically, the range is calculated from the round trip propagation delay, which is determined by measuring the phase shift in four coherent audio tones. This system is similar to the ranging equipment used at the INTELSAT earth stations. New integrated circuit (IC) technology has permitted individual tone transmission which was previously not available. The ranging tones are frequency modulated in both the up- and down-links in the INTELSAT system. However, in the COMSAT General system the tones are frequency modulated in the up-link and phase modulated in the down-link. Hence, new techniques are required to determine the phase shift of the earth station equipment.