Holdover And Keeping Approach Of Second-Class Frequency Standards

The second-class frequency standards (including high stability crystal oscillators and Rb atomic frequency standards) are used widely in clock systems in satellites and stations on ground, navigation and orientation devices, diagnose systems for electric power fault, synchronization equipments for communication networks, global positioning system and so on. These frequency standards are calibrated frequently. When the reference signals are lost or the transmission channels are cut off, the accuracy of the frequency standards would only depend on their own stability and aging. So a new method is proposed in this paper.The development and wide applications of the second-class frequency standards are introduced at the beginning of the paper, and then the environmental and physical factors affecting frequency accuracy and stability are analyzed, and also a new method to maintain the high frequency stability and high accuracy for a long time without the reference signals is presented in this paper. Through the updating of influences of the temperature and frequency shift on the frequency accuracy when the second-class frequency standards are being locked by the reference time signals, we can obtain the influences of the aging rate and environmental factors on the frequency accuracy, then we use the respond compensation values calculated to control the OCXO to maintain its high accuracy under the holdover mode. At the end, the research on the hardware design and algorithms of the second-class frequency standards system which has the holdover and keeping function are discussed in this paper. This new method will fill a domestic gap in technology area and provide the guarantee of precision for many users of our satellite system and the references of ground unify-time systems.