Measurements of Earth-station delay instabilities using a delay-calibration device

Delay calibrators were used to measure delay instabilities in the two-way satellite time-and-frequency-transfer Earth stations at NIST. Data from the calibrators suggests that the dominant source of Earth-station instabilities is group delay errors due to coherent interference and not physical-delay changes. The delay the calibrators measure is correlated utilize instabilities in the Earth stations but cannot always be used to improve the performance of the system because the correlation factor may be variable.