This paper describes the bunch by bunch transverse feedback implemented at ESRF. The first motivation of this project was to be able to cope with the constraint of the future operation of the ESRF with a stored current increased from 200mA to 300mA with a uniform or quasi uniform filling, but we were also interested in possible improvement of the operation with others filling patterns (16 and 4 bunches filling for instance). Our system uses a classical scheme: The signal coming from a set of button type electrodes is demodulated in a homodyne RF front end and processed in a FPGA DSP to derive a correction signal which is applied to the beam with a wide band stripline kicker. Depending on the filling pattern of the storage ring (uniform filling or filling with a small number of high charge bunches), different kind of transverse instabilities have been observed in the past, due to the resistive wall impedance, ion trapping or mode coupling. We have tested the effect of our system in these different situation and report also the results of these tests. These tests showed that our feedback system was efficient against all these instabilities by greatly increasing the current threshold for their occurrence both with null and positive values of the chromaticity.
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