Research Of Radio Compass Actuator System Based On FPGA

Radio compass is an important part of the airborne radio navigation system. It can automatically point out the heading angle, guide the aircraft to sail, and its technical performance directly affect the flight safety of the aircraft. Therefore, it is very necessary to carry out the accurate test of the aviation radio compass. Traditional radio compass test system consists of a signal source and an antenna to imitate the instrument, the whole system is large, the same is carried, and the price is high. And antenna simulator usually electromechanical frequency and phase modulation technology is adopted, prone to interference, resulting in the test system has testing azimuth angle fixed, low reliability, test accuracy and other shortcomings.In this paper, proposed a new a radio compass actuator design based on FPGA technology, on the basis of depth analysis of the compass working principle and the existing radio compass testing system. This new design uses USB interface as the communication interface between the host computer and this new compass actuator. The FPGA chip is the core of signal processing, and the DDS technology generates a variety of modulation signals. The zero-crossing detector method and amplitude comparison algorithm is used to generate the Low frequency synchronization signals of the same frequency and phase come from compass in the FPGA. In the output signal amplitude control module, I designed a numerically controlled attenuator which based on an DAC(AD5543),the AD5543 architecture uses a current steering R-2R ladder design. The numerically controlled attenuator has a large attenuation range,small size and low cost. By using this Attenuation circuit,the amplitude of the output signal from the compass actuator can contiuous varies between 50uv~1V.In this paper I also made analysis and research on DDS, which is used as core technology in compass actuator. The DDS spurious caused by phase truncation error was simulated, and the method to suppressing spurious such as phase jitter, noise shaping technology are also simulated. According to the simulation,it shows phase jitter can be well suppressed DDS spurious. In actual FPGA system this paper used an M sequence as scrambling code to make the phase jitter. This article is also designed the PC software based on Labview, In the PC software,this paper add an compass-error pre-processing module, this module can effectively counteract the compass’ error compensation, so the measured data can directly reflect the compass performance.Finally, according to the design scheme, the hardware system is made, and the simulation and performance test are carried out. Test results show that the proposed scheme can meet the performance requirements of a certain type of compass. Applying it to the test system of the radio compass can greatly improve the working efficiency and improve the accuracy and stability of the whole system, and can also reduce the cost and power consumption.