The dispersion relation for waves in a cold, magnetized plasma is discussed using the potential for the longitudinal part of the electric field. This clarifies wave emission from a conductor in low Earth orbit and should be useful in considering the far field and both hot plasma and nonlinear, near-field effects. General formulas for radiation impedance are directly obtained. For tethers a fundamental dependence on contactor size is discussed. Spherical and ellipsoidal contactors and an (anodeless) bare tether are considered. Simple arguments on nonlinear contactor effects lead to a surprisingly simple result from impedances off the Alfv¿n branch. ¿ American Geophysical Union 1995