Sardinia Radio Telescope: general description, technical commissioning and first light

In the period 2012 June-2013 October, the Sardinia Radio Telescope (SRT) went through the technical commissioning phase. The characterization involved three first-light receivers, ranging in frequency between 300 MHz and 26 GHz, connected to a Total Power back-end. It also tested and employed the telescope active surface installed in the main reflector of the antenna. The instrument status and performance proved to be in good agreement with the expectations in terms of surface panels alignment (at present 300 similar to mrms to be improved with microwave holography), gain (similar to 0.6 K/ Jy in the given frequency range), pointing accuracy (5 arcsec at 22 GHz) and overall single- dish operational capabilities. Unresolved issues include the commissioning of the receiver centered at 350 MHz, which was compromised by several radio frequency interferences, and a lower- than- expected aperture e-ciency for the 22-GHz receiver when pointing at low elevations. Nevertheless, the SRT, at present completing its Astronomical Validation phase, is positively approaching its opening to the scienti _ c community.