On the BRD4173A Radio Board the supply for the radio (RFVDD) and the sub-GHz and 2.4 GHz power amplifiers (SUBGRF_ON,SUBGRF_OP and PAVDD pins) is connected to the on-chip DC-DC converter. This way, by default, the DC-DC converter provides1.8 V for the entire RF section (for details, see the schematic of the BRD4173A)..