Northern Cross radioreceiver chains: the environmental test on the critical subsystem Marcantonio Catelani 1 , Valeria L. Scarano 1 , Roberto Singuaroli 1 , Stelio Montebugnoli 2 , Germano Bianchi 2 , Federico Perini 2 1 University of Florence, via S. Marta 3, 50139, Florence, Italy tel.+39 055 4796377/393, fax +39 055 494569, marcantonio.catelani@unifi.it , valeria.scarano@unifi.it 2 Istituto di Radioastronomia- INAF, via Fiorentina 3508/B, 40060, Medicina (Bo), Italy tel.+39 051 6965823, s.montebugnoli@ira.inaf.it , g.bianchi@ira.inaf.it , f.perini@ira.inaf.it Abstract –This research is developed in collaboration with the Istituto di Radioastronomia, Istituto Nazionale di Astrofisica (IRA-INAF) located at Medicina (Bologna), in the context of the BEST (Basic Element for SKA Training) project. SKA is the name given to a new generation radio-telescope that will have 1 km 2 of effective collecting area. SKA will be the most sensitive radio-telescope ever built that allows a deeper knowledge of the universe. After a reliability analysis we estimated the MTBF of the two approaches so we suggested the most reliable solution to implement. This work considers the most reliable solution for the radio astronomical signal receiver chains, the solution that conveys the analog signal through optical fibre. Since the reliability prediction indicated the front-end, installed on the focal line of the antenna, as the more stressed block by environmental and climatic factors, we recommended to perform the environmental tests on it. The whole tests plan has been characterized and some preliminary results are reported in the paper [1]. I. Introduction Two solutions of receiver chains have been taken into consideration. Their description is detailed in the [1]. Both these chains send an analog signal to the receiver room. The first solution does it through coaxial cable (used now in the Northern Cross receiver chain), while the other uses an optical link. The main advantages in using the optical analogue links, comparing the two solution above mentioned, are: wider band, lower signal attenuation, lower weight and dimensions, more strength and flexibility, better electric insulation and interferences immunity; this technological solution showed an higher level of reliability prediction. After a reliability evaluation [1], the optical link configuration was chosen for the implementation of the re- engineering of the Northern Cross Radiotelescope, it is based on the idea to transport the analog signals via an optical link directly from the front-ends (installed on the focal lines) to the processing room. This solution increases the reliability and makes easier maintenance activities, the major part of the processing hardware being indoor (in a temperature controlled and humidity sheltered room). This assures a complete protection from atmospheric agents, temperature variations, electrical discharge, etc. In addition this solution offers a direct accessibility to the equipment to simplify maintenance operations, with logistic and economical advantages. Moreover it would allow to obtain a simplified control, synchronism and LO signals distribution. The use of an analog fibre link needs to install an optical transmitter (laser) on the antenna focal lines after the first stage, including one LNA and two amplifiers with two pass-band filters between them. To remove the high noise figure introduced by the laser, an additional amplifier stage is needed to increase the gain before optical link. This optical signal reaches the processing room where the optical receiver reconverts it back to an electrical signal. The important aspect of this approach is that the LO and the synchronism signals are distributed only in the main processing room, where is installed the whole digital receiver. So we have the advantage of an easier maintenance and cheaper electronic devices can be used because they are in a sheltering room and then isolated from atmospheric discharges.