Straumann, T. Smith, S.R. JACoW Geneva, Switzerland 978-3-95450-177-9 10.18429/JACoW-IBIC2016-TUPG10 English 337-340 TUPG10 cavity detector timing operation dipole Contribution to a conference proceedings 2017 2017-02 http://dx.doi.org/10.18429/JACoW-IBIC2016-TUPG10 http://jacow.org/ibic2016/papers/tupg10.pdf Cavity BPMs commonly use the fundamental TM010 mode (excited either in the x/y cavity itself or in a separate "reference" cavity) which is insensitive to beam position as a reference signal, not only for amplitude normalization but also as a phase/time reference to facilitate synchronous detection of the signal derived from the position-sensitive TM110 mode. When taking these signals into the digital domain the reference and position signals need to be acquired by a synchronous clock. However, unless this clock is also locked to the accelerating RF, absolute timing information is lost which affects the relative phase between reference and position signals (assuming they are not carefully tuned to the same frequency). This contribution presents a method for estimating the necessary time of arrival information based on the sampled reference signal which is used to make the signal detection insensitive to the phase of the digitizer clock. Running an unlocked digitizer clock allows for considerable simplification of infrastructure (cabling, PLLs) and thus decreases cost and eases maintenance.