| Solar eruptions can affect human activities in a catastrophic way.Based on multi-band observations,we can predict solar activities earlier,and reduce the hazards caused by solar activities.Radioheliographs can provide spatial information of solar radio bursts.In order to obtain high quality imaging,a high precision time-frequency synchronization is required.It is of great significance to design and build a time-frequency synchronization system which can be used to maintain the high-precision time-frequency synchronization of Radioheliographs.In this research,a fiber-based time-frequency synchronization system for Radioheliograph is investigated.First,a star-shaped time-frequency synchronization scheme suitable for radioheliograph is designed based on the shape of the proposed array,then we implement and test it.Then,the influences of the environmental conditions and devices on the system performance are tested.Finally,the delay error is largely compensated to improve the precision of time-frequency synchronization,and the test system is extended to multiple links.The following are the main results.(1)For the problem of time frequency synchronization in Radioheliographs,a star-type time-frequency synchronization solution is designed based on the wavelength division multiplexing(WDM)technology Round-trip method.According to the design,the time-frequency synchronization system is built,and realized the function of synchronous transmission of time-frequency signals to multiple receivers.(2)To determine the effect of devices on the performance of the time-frequency synchronization system,the effect of environmental conditions and devices on the time-frequency synchronization is tested.It is found that the time interval between different channels is mainly caused by the length difference of fibers,and the temperature is the most important factor that affecting the stability of this time difference.When the temperature is around 10℃,the fiber device and the whole time-frequency synchronization system is the most stable.When the temperature increases or decreases the deterioration of time frequency synchronization gets worse.(3)To improve the time and frequency synchronization accuracy,a jumper is used to compensate the fiber length difference between links.Before the implementation of the compensation,the measured timing accuracy is 6.5 ns,and the timing accuracy is improved to about 2 ns by compensating with the jumper.This result proves that compensating the optical path difference can significantly improve the time-frequency synchronization accuracy.In this thesis,a star-shaped time-frequency synchronization scheme for radioheliographs is designed,and achieved the function of synchronous transmission of time-frequency signals.Then a timing accuracy of 2 ns is achieved by jumper compensation.This design has the advantages of low cost and high accuracy,and also provides a reference for other time-frequency synchronization systems at kilometer level. |
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