This paper presents results from a numerical study of the generation of magnetic field-aligned currents with a perpendicular scale size of the order of 10 km and a magnitude of a few ¿A/m2 at 100-km altitude by the ionospheric feedback instability triggered and controlled by the heating of the ionospheric E layer with a powerful HF transmitter. Simulations reveal that the development of the feedback instability inside the global magnetospheric resonator significantly depends on both the conductivity of the heated ionosphere and that of the conjugate ionosphere. Investigations of different temporal modes of the heater operation show that the heating has a maximum effect on the instability growth rate when it is modulated with an eigenfrequency of the coupled magnetosphere-ionosphere system. This frequency is sensitive to the ionospheric parameters, in particular to the magnitude of the background electric field inside the ionospheric E layer, and it can be 10 times lower that the eigenfrequency of shear Alfv¿n waves standing along the magnetic field lines between the ionospheres.