Progress in portable instrumentation for time source verification and analysis

The calibration of the internal GPS-slaved reference clock of a portable time measuring instrument has been carried out using GPS Common View and we report on the subsequent direct measurement of the reference accuracy and stability over different time periods. The measurement architecture has been extended to include Grand Master time sources that conform to IEEE Std 1588 PTP (Precision Time Protocol). Time-code interpretation, network packet capture and time-stamping are performed by a programmable logic array (FPGA) and network transceiver (PHY) combination. This approach eliminates sources of imprecision which are found in traditional software based network package capture systems. Once captured, packets are interpreted by a specialized PTP protocol stack capable of automatically classifying PTPv1 and PTPv2 without the involvement of the operator.