The aim of this paper is to show a simple method to characterize a common mode choke (CMC). For the accurate 3D modeling of a CMC, it is essential to know the frequency dependent permeability of the core. To establish the electromagnetic properties of the core of the choke, a simple impedance analyzer and a partly disassembled CMC is enough. The impedance measured this way is suitable to express the permeability, that can be subsequently used to build an accurate coupled 3D-circuit model of the CMC. This model can be utilized to examine inductive and capacitive couplings between the choke and other nearby placed filter components, e.g., capacitors.