GENERATION OF RF FREQUENCY AND PHASE REFERENCES ON THE FAIR SITE

Based on the Time Synchronization System (BuTiS) [1] local analogue radio frequency reference signals (RF references) like the particle revolution frequency and their multiple harmonics will be generated. These references are used to control the phase of the accelerator cavities at altering harmonics of the bunch revolution frequency. Delays or phase shifts from the FAIR-Centre to the references at the BuTiS endpoints are already compensated by the BuTiS receivers. Phase shifts from the RF reference generators to LLRF electronics can be compensated by controlling the output phases of the DDS modules of the RF references. However, phase shift delays of multiple harmonics at the same interconnecting electrical path are not identical at the same time. Configurable electronics [2] manage phase calibration of the RF references to their endpoints. In most cases, the calibration depends on the frequency and the harmonic number of the RF reference, aging as well as on thermal effects. The electrical length and impedance mismatches of interconnecting cables for phase control loops can be compensated. This is an important feature, in particular if control loops are switched between different harmonic frequencies.