This report describes a LLRF system developed at Lancaster University and an experiment undertaken at the STFC Daresbury Laboratory by Cockcroft Institute Staff to validate an approach to phasing the crab cavities for the International Linear Collider. The work has involved the manufacture and processing of a pair superconducting cavities, the development of a vertical cryostat facility, the development of a digital control system for each cavity and the development of an interferometer. In a test conducted during August 2008 it was demonstrated that an RF interferometer with digital phase detection and digital cavity controllers can lock a pair of superconducting cavities having realistic levels of microphonics such that r.m.s. phase errors are less than 120 millidegrees at 3.9 GHz. 1. Engineering Department, Lancaster University, Cockcroft Institute, Lancaster, LA1 4YR 2. ASTeC, STFC Daresbury Laboratory, Daresbury, Warrington, Cheshire, WA4 4AD, UK EUROTeV-Report-2008-073 December 2008 2 of 67 3.