Design of the GNSS Clock Frequency Abnormal State Emulator

Clock signals is the reference signal of the frequency synthesis signal acquisition and the time synchronization in the GNSS. The clock frequency abnormal state make a direct impact of signal integrity monitoring. The theoretical analysis and software simulation are the commonly way to studying on the abnormal state clock frequency signal and it's impact for GNSS system applications. In order to test and evaluate this impact, The paper designs and implements navigation clock abnormal state impersonation system. And it designs a clock abnormal impersonation emulator, based on the simulation software Mat lab and the Programmable DC Power Analyzer Agilent N6705 and high-precision adjustable bias voltage of Voltage Controlled X'tal Oscillator (VCXO). Firstly, through the Mat lab simulation to generate a specific pattern of tiny voltage control words, a particular feature of the control voltage generated by the programmable DC power analyzer, adjust the controllable bias voltage of VCXO, then the corresponding micro-controllable variation state superimposed on the main clock, so that the clock contains various abnormal state, at last using Frequency Counter SR620 to measure the output of the system to analyze the results. The simulation and experimental results show that the system can correctly emulate the output frequency clock rate of the abnormal state, including white-noise characteristics of the variable amplitude fluctuations. Furthermore the size, duration, amplitude of the above-mentioned characteristics can be controlled adjustable. The clock abnormal state impersonation emulator can be widely used in the testing and emulating of abnormal clock frequency signal for GNSS system.