Design and Implementation of a Time Frequency System with Auto-Switching Clocks at a VLBI Station

As a major equipment of a VLBI station, an effective time frequency system supplies stable and reliable time/frequency data for the station. The signals from such a system will directly affect the quality of data processing. The key device in a time frequency system is its hydrogen clock. In order to ensure accomplishing observational tasks, a VLBI station is engineered to be equipped with at least two hydrogen clocks. Using multiple hydrogen clocks requires switching between different routes of signals. A long duration conventionally needed for switching will cause interruption of signals, and make it necessary to replace the data-processing model after a switch. In the worst cases signal interruption can result in loss of data in several hours. It is rather worth to study fast and efficient approaches to switch hydrogen clocks. In this paper we present a design of a cost-effective time frequency system with auto-switching hydrogen clocks. We also describe our implementation of the system and its practical effectiveness.