Brajnik, G. Bassanese, S. Cautero, G. Cleva, S. De Monte, R. JACoW Publishing Geneva, Switzerland 978-3-95450-201-1 10.18429/JACoW-IBIC2018-TUOC01 English 190-195 TUOC01 FPGA controls electron feedback Ethernet Contribution to a conference proceedings 2019 2019-01 https://doi.org/10.18429/JACoW-IBIC2018-TUOC01 http://jacow.org/ibic2018/papers/tuoc01.pdf In this contribution, we describe the advantages of the pilot tone compensation technique that we implemented in a new BPM prototype for Elettra 2.0. Injecting a fixed reference tone upstream of cables allows for a continuous calibration of the system, compensating the different behaviour of every channel due to thermal drifts, variations of cable properties, mismatches and tolerances of components. The system ran successfully as a drop-in substitute for a Libera Electron not only during various machine shifts, but also during a user dedicated beamtime shift for more than 10 hours, behaving in a transparent way for all the control systems and users. The equivalent RMS noise (at 10 kHz data rate) for the pilot tone position was less than 200 nm on a 19 mm vacuum chamber radius, with a long-term stability better than 1 um in a 12-hour window. Two main steps led to this important result: firstly, the development of a novel RF front end that adds the pilot tone to the signals originated by the beam, secondly, the realisation of an FPGA-based double digital receiver that demodulates both beam and pilot amplitudes, calculating the compensated X and Y positions.