Power modulation experiments are a well known tool to investigate electron heat transport and have been widely used in conventional L-mode or H-mode plasmas. In this paper new results are presented of power modulation experiments in JET plasmas characterized by strong electron and ion Internal Transport Barriers (ITB). The modulated power source is RF ICRH power in mode conversion scheme, which takes place in D plasmas with 3He concentrations of 10-20%. This provides a source of direct, localized and controllable power to electrons, suitable for transport studies of electron ITBs. The ECE diagnostic allows time and space resolved measurements of the Te perturbation. 3.25-3.6T, 2.6-2.9MA plasmas with neo ~3-51019 m-3 have been used. LH preheat (2-3MW) was applied to achieve configurations with deeply reversed magnetic shear (s). The ITB is located in the region of negative s. Up to 18MW of NBI power and 4MW of ICRH power modulated with half depth at 15-45Hz with duty cycle ~60% were applied. The MC power has been localized either at the ITB layer, providing a heat wave generated in the ITB region, or just outside it, providing a heat wave that travels towards the ITB. The ITB is mainly sustained by NBI power, but when the RF is deposited inside the ITB radius, the good localization of power allows to reach outstanding plasma performance, with Ti0 ~24keV, Te0 ~13keV, ne0 ~5 1019 m-3, at an additional total power level of 15MW. The equivalent QDT is estimated to be ~0.25 in these discharges.