Remote Frequency Calibration Using GPS Carrier-Phase Observation Measurement at TL

摘要

Because the GPS carrier-phase observation measurement is very precise in frequency transfer, it can be used to estimate performance of a remote frequency reference with respect to the national frequency standard. TL has already set up a prototype system for this purpose. The stability and accuracy of a DUT (device under test) at a remote site with traceability to TL's frequency standard could be obtained after data processing. The prototype system includes the master site (herein at TL) and the remote site. At the remote site, the equipped GPS receiver runs with a DUT as its frequency reference. By performing the time difference (differences between two epochs) on carrier-phase observations, the DUT's frequency offset with respect to the GPS frequency standard can be estimated. At the master site, the GPS receiver is referenced to TL's frequency standard and the time difference and carrier- phase single difference (differences between two receivers at TL and the remote site) are performed at postprocessing. The frequency offset of the DUT relative to TL's frequency standard can be estimated in this way. Observations from the remote site could be sent to TL via the Internet. As for the system arrangement, the IGS (International GPS Service) site TWTF at TL serves as the master site and a single-frequency GPS receiver is adopted at the remote site to cost down expenses of system set up. Data analysis is done by the lab-developed software. A common-clock short-baseline test (using TL's frequency standard) and a 270-km baseline test (using a high-performance 5071A cesium clock as the remote frequency reference) were carried out to find the system's performance. In the 270-km baseline test, a dual-frequency GPS receiver was also used at the remote site for comparison.