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The complex antenna factor (CAF) of a dipole antenna with a balun can be determined from the effective length and the input impedance of the antenna element and the S-parameters of the balun. The effective length and the input impedance are calculated by a numerical method such as the method of moments. The S-parameters are measured using a network analyzer with its thru-, reflect-, and line-conditions (TRL) calibration. Alternatively, the CAF can be determined by a modified three-antenna method on a ground plane. In the present paper, the systematic uncertainties of the two methods are estimated in the frequency range of 30-1000 MHz in order to clarify the potential for application of the two methods and to determine areas for improvement. The CAF values determined by these two methods are compared, and the results of this comparison indicate the validity of the uncertainty estimations. In the measured balun method, the TRL measurement should be improved in the low-frequency range (30-100 MHz), and in the three-antenna method, the antenna positioning should be improved.