Impedance mismatch influence at internal delay of navigation signal simulator calibration

This paper is devoted to navigation signal simulator calibration. The description of uncertainty estimation of inter- nal signal simulator delay, which is caused by impedance of measurement equipment (navigation signal simulator, analyzer and measurement cable) mismatch, is shown in the paper. The aim of research is to get expression to count uncertainty of simulator internal delay and to give its quantitative assessment. The uncertainty is caused by presence of reflected signal at the input of signal delay estimation algorithm. Reflected signal has place because input/output impedances of measurement equipment are different. The simplified mathematical model of signal at the signal delay estimation algorithm input is given. Correlation algorithm work for given model of signal has been analyzed. Two expressions for systematic uncertainty of delay estimation count have been derived and their inaccuracy has been esti- mated by means of modelling. The first expression is universal for all variety of navigation signals; the second is more accurate and takes into account spectral characteristics of the concrete navigation signal. The quantitative assessment of uncertainty, based on modern measurement equipment is given - at the length of measurement cable about one meter systematic uncertainty can reach 100-150 picoseconds. Conclusion was made, that at modern requirements to navigation signal simulators calibration, impedance mismatch must be taken into account. The information, mentioned in this paper, can be used at internal delay of navigation receivers’ estimation when receivers are calibrated by means of navigation signal simulator.