Electromagnetic radiation from sources immersed in a cold magnetoplasma is analyzed by the use of ‘principal-polarized’ wave coordinates; and the wave fields, the mean complex radiated power, and the Poynting vector are systematically expressed in terms of ‘polarized’ wave modes. For each polarized wave mode, the medium is effectively isotropic, since the Fourier-transformed wave equation for each principal mode is decoupled and is similar to the one obtained from the usual scalar Helmholtz operator. In application of the theory, consideration is made of the radiation resistance of a linear electric antenna of moderate length oriented both parallel and perpendicular to the static magnetic field. Approximate closed form expressions for the radiation resistance are obtained for the VLF frequency range by using a plasma model appropriate to the magnetosphere. These approximate closedform expressions are compared with the results obtained previously by other workers using a quasi-static approximation, and it is shown that excellent agreement exists between the two methods of analysis. It is concluded that the quasi-static approximation can accurately predict the radiation resistance of a linear antenna in the magnetosphere, given certain moderate restrictions on the antenna length.