Absolute Calibration of GPS Time Transfer System at NTSC

GNSS time transfer is the main technology currently used in UTC generation. GNSS reception chains need to be calibrated for ensuring accuracy and long-term stability of time links. This paper presents the recent absolute calibration at NTSC. The receiver is calibrated using a satellite simulator, and the antenna calibration is done using a specific anechoic chamber with Vector Network Analyzer (VNA) signals. The results show that the calibration uncertainty is 2.4 ns. We use another receiver, NTP3, was relatively calibrated in 2018 to evaluate the calibrated results. The calibration uncertainty of NTP3 is 3.2 ns from BIPM website. We obtain the common clock difference (CCD) between NTP3 and NT06, and the mean of GPS P3 CV result is 3.95 ns, within the total uncertainty of 4 ns.