The ongoing progress of the technology using signals transmitted from satellites to ground stations or end users requires a development of all the devices which are involved in the generation, processing and transmission of the in the meantime very complex signals. A very clear generated signal should not be made worse during the amplification. Traveling wave tubes (TWT) for satellite application are based on a well known physical theory. Thales Electron Devices (TED) demonstrated that the tube is still a very flexible and reliable amplifier with a large space proven heritage which can be used not only for standard CW operation but also for the transmission of very sensible data like modulated signals in the L-band for navigation systems -successfully demonstrated by the first in-orbit tests of Giove-A Galileo Satellite