Earth station errors in two-way time transfer

We have investigated the earth station errors in two-way time transfer. A 3.7 m earth station and a very small aperture terminal (VSAT) 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 (RX) delay for the 3.7 m NIST earth station was found to be -150 /spl plusmn/30 ps//spl deg/C and the temperature coefficient for the transmit (TX) delay was -50/spl plusmn/10 ps//spl deg/C. The overall temperature coefficient for the earth station was 100/spl plusmn/30 ps//spl deg/C. Aside from environmental errors there are apparent changes in delay due to characteristics of the modulation/demodulation scheme. Apparent delay changes due to non-linearity effects in the earth station were as high as 10 ns. The errors due to code dependence and third code interference were as high as 3 ns.