Portable Instrumentation for Time Source Verification and Analysis

The architecture and principles of operation of a new type of portable, battery-powered measuring instrument for precise time source performance analysis are described. Potential applications include the measurement of common time sources, such as simple pulsed systems, asynchronous serial data streams, modulated and unmodulated time-codes and particularly network time servers using Network Time Protocol (NTP) or Precise Time Protocol (PTP). New techniques for high precision 100Mb/s Ethernet packet timing as well as for modulated carrier time-code extraction are described showing how the accuracy of clocks providing these sources can be fully assessed automatically in the field with laboratory precision. The employment of a GPS receiver and antenna within the same compact package to provide the synchronization and disciplining of an internal rubidium oscillator is presented, together with some results of its performance in a typical time source measurement project. This portable clock can maintain reference time with high accuracy when GPS signals are no longer available during the verification of a time source. The method of time comparison using precision clock signals from the rubidium oscillator in conjunction with interpolation to sub-nanosecond resolution is outlined; the principal advantages of the method described are its seamless and continuous time measurement capability over a full +/-500ms range to a resolution of 100ps directly related to the best averaged information from GPS satellites. Traceability of the instrumentation is established and maintained by the use of GPS Common View calibration.