The oscillatory pattern of the electrostatic potential radiated in a hot magnetoplasma at frequencies &ohgr;<min (&ohgr;p, &ohgr;c) is examined in terms of the intrinsic diffraction phenomenon: &ohgr;pand &ohgr;care, respectively, the electron plasma and cyclotron frequencies. It is shown that the potential maxima are located on equally spaced cones parallel to the resonance cone. The spacing of these cones, measured along the ambient magnetic field, is simply related tok∥I, the parallel component of the largest unattenuated wave vector. The consistency of these features with experimental observations is shown. A method of measurement of the electron temperature is derived.