A modification of Z12T metronome time transfer system

We modified one Z12-T Metronome geodesic GPS receiver time transfer station by adding a time interval counter (SR-620) to measure the time difference between its external reference 1 PPS and 20 MHz frequency inputs. The time differences were compensated into the pseudorange measurement of its RINEX file. In consequence, the reference time of the modified pseudorange of RINEX and REFGPS of CGGTTS are re-defined to be the system's external 1 PPS reference, no more its external 20 MHz frequency input.