Delay Difference Calibration of TWSTFT Earth Station Using Multichannel Modem

Delays in signal transmission and reception paths of an Earth station must be calibrated accurately, and their variation should be reduced in the two-way satellite time and frequency transfer (TWSTFT). We have developed a portable TWSTFT station using a modem built by the National Institute of Information and Communications Technology (NICT) and performed calibration between NICT and Telecommunication Laboratories. An uncertainty of about 1 ns in the differential calibration was achieved. In addition, we have monitored the delay variation in the Earth station using a measurement system installed at NICT to improve accuracy of the TWSTFT. The contributed instability was 50 ps/day