We have investigated the earth station errors in two-way time transfer. A 3.7-m earth station and a very small aperture terminal earth station were used in these experiments along with a transponder located on a mountain about 10 km away. The temperature coefficient of the receive delay for the 3.7 m NIST earth station was (-150/spl plusmn/30) ps/K, and the temperature coefficient for the transmit delay was (-50/spl plusmn/10) ps/K. The overall temperature coefficient for the earth station was (100/spl plusmn/30) ps/K. Aside from environmental errors there are apparent changes in delay due to characteristics of the modulation/demodulation scheme. Apparent delay changes due to nonlinearity effects in the earth station were as high as 10 ns. The errors due to code dependence and third code interference were sometimes as high as 3 ns.
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