a) Orbital modulation of the electron density assumed in the model, as defined in Sect. 3.1. The two ejections are given at Φ = 0.35 and at Φ = 0.58. b) The maximum value of the Lorentz factor γ of the electrons as a function of the position l along the jet for the two ejections. The black curve is a plot of the minimum γ (Eq. (27)) necessary for the production of radio emission at 15 GHz for an initial magnetic field B₀ = 5 G. The intersection point of the black curve with the red and blue lines defines the length of the jet at periastron and that of the jet towards apastron, respectively.