Directions of the magnetic field and of the radio waves emitted in the source frame: the wave vectors are along a cone of summit angle α_s, and of an axis parallel to the magnetic field B_s. The wave vector position on that cone is parametrised by the angle Ψ_s. The inclination of the magnetic field with the wing axis Oz is λ_s. The cylindrical angular coordinates θ_s and ϕ_s of the wave vector are defined relatively to the z axis. As in Fig. 1, the star (at Ψ_s = 0) marks the angle of emission of the most intense CMI waves.