Experimental study of the upper hybrid resonance cone radiated by a point source shows that the potential is mostly due to the so-called main mode, whenever the frequency is not too close to the upper hybrid frequency. This is in agreement with the extensive calculation of the potential based on the solution of the electrostatic dispersion relation. Detailed analysis, both theoretically and experimentally, of the oscillating pattern related to thermal effects shows that the structure of the upper hybrid resonance cone is correctly described by the intrinsic diffraction model.