Realizing UTC(NIST) at a remote location

Abstract

I will describe the backup time scale system that I have constructed at the site of the NIST radio stations near Fort Collins, Colorado, and I will compare its performance with the primary ensemble in Boulder. The Fort Collins system is designed to be a backup for the Boulder system and is intended to support all of the NIST time services should the primary scale become unavailable for any reason. The backup time has a number of unique problems and requirements, and I will discuss the design considerations that I used to address these issues. The backup scale tracks UTC(NIST) in frequency with an uncertainty (measured by the Allan deviation of the difference) of about 1 × 10−14 by use of administrative steering that is applied not more often than once per week. The corresponding time deviation is less than 1 ns for all averaging times less than 1 week, and the peak time difference between UTC(NIST) and its backup realization is less than ±25 ns and is generally much better than this value. This is much better than would be needed for supporting the radio stations, the digital time services (ACTS, a time service that provides time in a digital format using dial-up telephone lines, and the Internet services) and the Frequency Measurement Service. Its frequency stability and time accuracy would not be adequate for the most demanding users of the Global Time Service and for international time and frequency coordination. The primary limitations to the performance of the backup time scale are caused by environmental perturbations, especially temperature and supply voltage, and the existing hardware could probably support all of the NIST services if the environment were improved.