We propose to detect and resolve the candidate radio counterpart of an ultraluminous X-ray source (ULX) at the outskirts of NGC 1313. This ULX is surrounded by a huge ionized nebula. We expect to find a corresponding synchrotron radio bubble, possibly inflated by a jet from the black hole, with additional core emission. By combining radio, optical and X-ray information, we shall determine the energy balance of the accreting black hole: how much gravitational power is radiated by disk and corona, how much is advected, how much is carried out by jets and winds. Resolving radio core and lobe emission will give us both the instantaneous balance of power and the average energy budget over the source lifetime. In turn, this will test multi-band spectral models and allow us to constrain the black hole mass and the physical nature of this mysterious class of sources.