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To overcome the analog technology limits a fully Digital Vector Voltmeter has been developed and characterized showing that the apparatus gives better performances than commercial equipment. In particular it can perform measures up to half GHz RF signals, obtaining a phase accuracy up to 0.03Â° including the linearity error, at output rate of 2 MHz. The apparatus covers a full dynamic range of 80 dB with the accuracy depending on the input level. The apparatus is based on a fixed FPGA Hardware architecture allowing to host different firmware to cope with various applications. In particular the apparatus has been adapted to two different plasma diagnostics of the FTU ENEA Frascati Tokamak: an RF reflectometer and a laser interferometer. Both diagnostics need a difference of phase measure between an IF signal and a reference, but in quite different conditions. The same hardware system has been used for both diagnostics just replacing its firmware to fulfill the requirement of the detection.