FIG. 2: (top) integrated power as a function of the out-of-plane magnetic field. The field is swept from negative to positive values. H$_{c}$ is the critical field at which microwave oscillations occur for I$_{dc}$ = 3.2 mA, H$_{sw}$ is the field at which the vortex core reverses. (bottom) frequency as a function of the out-of-plane magnetic field. Blue dots : I$_{dc}$ = 1 mA, red dots : I$_{dc}$ = 3.2 mA. field is attributed to a deformation of the energy landscape by grains. For H$_{sw}$ = + 5 kOe, a large jump in frequency occurs due to the reversal of the vortex core polarity. After the switching, it becomes aligned to the applied field and to the polarizer like in the case of large negative fields (zone I). The reversal of the core polarity, associated with the abrupt change in frequency and the recovery of the oscillations, is well reproduced in the simulation (see Fig.3). It is worth emphasizing that a symmetrical behavior is obtained when saturating first at large positive H$_{perp}$ and then decreasing the field toward negative values. As already mentioned, for negative currents, the condition to get large oscillations is that the vortex core polarity and the out-of-plane component have opposite signs. The measurement of the integrated microwave power for I$_{dc}$ = -5 mA as a function of H$_{perp}$ , 7