The Research On The Method Of Data Acquisition And Monitoringthe Radio Frequency Signalbased On National Instruments

In the field of radar,weather,prediction on earthquake,aviation,spaceflight,communication and accelerator,the signal has an important role.These signal shave some characteristics with strong real-time,high data rates,large volume of data and handling complex.The method of data acquisition and monitoring in RF signal based on National Instruments can be collected,monitored and recorded the RF signal amplitude and phase.And this can be improved the running state of the real-time monitoring of the RF signal,and judged the influence on the condition of the system.This has engineering reference value.The principle of signal sampling has reviewed in this paper,and then the theorem on Nyquist sampling and the theory of IQ sampling have been introduced.The principle on different modes of modulation and demodulation has been discussed and the RF signal has need to be processed before sampling,such as the frequency of the mix signal,the frequency conversion up and down,as well as the algorithm on FIR filter after sampling.The dynamic range and phase accuracy have compared after the modules of the IMO-08-412,AD8302 and self-built IQ demodulation circuit have been tested,self-built IQ demodulation circuit has been chosed to achive the detection.Aiming at the influence of inherent errors such as DC bias,amplitude imbalance and phase imbalance on the accuracy of the RF signal amplitude and phase,a software calibration algorithm based on IQ demodulatio n technology is adopted to improve the amplitude stability and phase precision.The accuracy of amplitude and phase have been effected by the intrinsic errors in hardware,such as DC offset,the imbalances of amplitude and phase.A calibration method for IQ demodulation technique has adoped to improve the accuracy of amplitude and phase..Then the performance of the RF front-end board has been tested.When the power of local oscillator signal has meet the requirements and the power of RF signal is-10 d Bm,the relationship of phase is strict linear and the output of the IQ signal can to be the perfect circle after calibration.While the power of RF signal between-26 d Bm to-6d Bm,the accuracy of amplitude and phase in the radio frequency signal has been promoted to ±0.7% and ±0.25 o after calibration.The hardware system on the signal acquisition and monitoring for the four-channel IQ demodulator has been designed.The system has the existed PXI controller and data acquisition card(PXI 8108 controller and the PXI 6251).The noise of PXI6152 is the less than 0.03 V,and this is no impact on the accuracy.Finally,the system has been tested.When the power of radio-frequency and local oscillator signals are-12 d Bm and +7 d Bm,the IQ voltage value acquired by PXI625 1 can be amplified nearly 10 times in amplitude after calibration,and this can be improved the performance on system's anti-noise.The stability of voltage signal,which output of IQ demodulator circuits,is less than ?±1.5% and ?±0.8o after calibration.It's good performance and satisfied the requirements of the measurement.Four-channel IQ demodulation of the RF signal at synchronous has been realizes in this paper,and the performance of cost-effective,compactness and maintenance convenience in the hardware system have been improved.At the same time,the calibration algorithm is adopted to improve the stability of amplitude and the accuracy of phase.And this is a way to implement of data acquisition and monitoring for RF signal in the RF field.