Absolute Calibration of Time Receivers with DLR's GPS/Galileo HW Simulator

Kurzfassung

A usual way for time transfer between atomic clocks operated at different locations is the use of the well known GNSS Common View technique. This technique is based on time receivers measuring the time differences between the connected atomic clock and the GNSS satellite clocks. The obtained results can be used for time scale generation such as UTC or TAI. In order to produce a very accurate time scale from all provided time differences measured with different GNSS time receivers the accurate calibration of them is essential. In the last years two main methods for time receiver calibration were proposed. One is to compare the obtained time differences relative to a calibrated receiver. Following the second method one performs an absolute calibration of time receivers using a GPS HW simulator. In this paper the absolute calibration of time receivers with DLR’s GPS/Galileo HW simulator is analyzed and described in detail. The primary step is to calibrate the simulator itself. In this context the most important facts and values which have to be measured are explained. After the calibration of the simulator the receiver is fed with satellite signals generated by the simulator belonging to a standard GPS satellite constellation to determine the absolute offset of the receiver (internal delay) compared to the simulator output. Additionally the precision of a combined GPS/Galileo receiver for frequency transfer is investigated and determined.