Standardized radiation measurements can be simulated by various numerical or analytical approaches. In this article, a transfer function method is proposed for a fast and accurate antenna voltage prediction. Assuming that the interference source can be characterized as a linear Norton equivalent current source, its internal admittances and source currents are determined from measurements made with a vector network analyzer and an oscilloscope. The setup of the radiation measurement is described as a transfer function using its scattering parameters. A system of equations is set up with the multiport theory and solved for the antenna voltage, which is fed into a spectrum analyzer model. The result is compared to a measurement in a fully anechoic chamber. The method is extended to interference sources with stochastic signals, and, in the course of this, an approach for the estimation of the radiation measurement is developed. A dc motor is used as an application example.