| In the field of time-frequency transfer, the long distance transmission from a few dozen to several thousand kilometers generally use wireless or fiber, and the short distance transmission from a few meters to several kilometers generally use coaxial cable. But due to the characteristic of the conductor itself and the limitations of cable structure, coaxial cable will reduce the precision of time-frequency signal during transmitted. For shorter distances less than one hundred meters, the frequency accuracy is less reduced. But when the transmission distance over one hundred meters and under several kilometers, the quality of the time-frequency signal is several reduced, especially the frequency signal may not be effectively identify.In order to improve the accuracy when the coaxial cable is used to transfer the time-frequency signal, traditionally a stationary a stationary path delay is used ad main error sources to be corrected. However, because of the influence of measurement conditions, the path delay may be dynamic change, it affects the performance of time signal obtained by user.Therefore, a method of transferring is been restoring the high-precision time-frequency signal based on coaxial cable is proposed by the paper, and then a prototype has been develops to be used to validate it.The first, the transmission characteristics of coaxial cable is studied. The specific impact of these characteristics for the rectangular pulse signal is also pointed out. Then the paper mainly studies the time signal bidirectional transmission principle and the time-frequency-signal high-precision restoring principle; Base on the above principle, the method of transferring and restoring the time-frequency signal in the hundred meter scale base on the coaxial cable is proposed; In addition, time frequency signal recovery circuit board and the control center software is designed and developed; Finally, the performance test and analysis system is designed to measure and analyze the stability and accuracy of the time-frequency outputted by the prototype, and to test the maintain performance in case of where the cable is interrupted.Test results show that the proposed method of transferring and restoring the high-precision time-frequency signal based on coaxial cable is practicable. After the time-frequency signal is transmitted to 300 m distance by using the method, It is found through the analysis of measurement data that the accuracy of time signal is within 125 ps, and stability is less than 500 ps,and the 1s carrier frequency stability is 3.621e-12,and the 1000 scarrier frequency stability is 9.0e-13,and frequency deviation of 1000 s is 2.5e-14. Using the proposed method, not only the high-precision frequency signal is transmitted has been realized. The signal keeping function is developed to enhance the reliability of the system.The output of system will not be affected by signal input interruption of a short time. |
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