ULISS: AMobile cryogenic ultra-stable oscillator

We recently demonstrated a Cryogenic Sapphire Oscillator (CSO) presenting a short term frequency stability better than 3×10^-15 for 1 s ≤ T ≤ 1,000 s and achieving 4.5×10^-15 for one day integration. This CSO was designed and built in the frame of a research contract funded by the European Space Agency (ESA). It incorporates a pulse-tube cooler instead of a bath cryostat - thus eliminating the need for regular supplies and manual transferring of liquid helium. The advent of reliable and cryocooled CSO opens the possibility to implement such an ultra-stable reference not only in metrological laboratories with liquid helium facilities but also in remote sites like base stations for space navigation, VBLI antenna sites, ... In a new project: ULISS (Ultra-Low Instability Signal Source), funded by Regional and European Institutions, we are devel-opping a new cryocooled oscillator specially designed to be transportable. The ULISS oscillator will be compared and tested in various laboratories, observatories and industrial companies throughout Europe. In this paper we present the status of the ULISS project and the last frequency stability and phase noise characterisations of the current CSO working for more than one year in our lab.