Remote Frequency Calibration Using GPS Carrier-Phase Observation Measurement at TL
NATIONAL STANDARD TIME AND FREQUENCY LAB TAOYUAN (TAIWAN)
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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 TLs 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 DUTs frequency offset with respect to the GPS frequency standard can be estimated. At the master site, the GPS receiver is referenced to TLs 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 TLs 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 TLs 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 systems performance. In the 270-km baseline test, a dual-frequency GPS receiver was also used at the remote site for comparison.
- Test Facilities, Equipment and Methods