• W. Anders, A. Heugel, S. Klauke
  Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
• H.-G. Hoberg, G. Mielczarek, T. Westphal
  BESSY GmbH, Berlin

Most proposals of fourth generation light sources are based on cw operated sc liancs used in a FEL or ERL. The required RF power is strongly amplitude modulated due to the fact, that microphonics in the sc cavities plays an importand role. The requirements for the stability of the RF field in the cavities are better than 0.1 deg phase and better than 0.1% amplitude. At the HZB a modular RF transmitter was developed with FUG, that can be used for IOT tubes for different power levels and frequencies. Special attention was taken to the stability in the case of AM modulation.