Planck-LFI CPV: Functionality Reference Point

Abstract

This document describes the results from the Functionality Reference Test (FRT) The FRT is composed by two parts, devoted to different tasks: The first part is identical to the CRYO 02 ( ) : it is devoted to check the functionality of radiometers in all the possible phase switch and 4KHz combinations, after the HYM Tuning (that was considered a possible source of stress for radiometers) and to compare with it. In particular, the LNAs drain currents will be compared, together with the noise properties as 1/f, white noise, spikes. The output voltage can be compared just roughly considering the sky signal, because the ref signal decreases due to 4K cooler cooldown: this rough comparison must take into account possible differences in the SCS temperature ( driving the FPU temperature and hence the LNAs gain) and the radiometers Isolation ( the signal leaking from the Reference loads and mixing with the Sky signal is proportional to the Reference Load temperature) . The second part is identical to the same test performed in CSL (Liege , 2008) , but is performed with the LNAs bias set to the final configuration outcome from the HYM Tuning. This test, similar from the procedural point of view to the CRYO 01, is devoted to set a reference point for the future of the survey, characterizing one by one all the LNAs measuring both the scientific output and the bias ( drain currents). This is operation can be repeated at any time during the survey, with a minimum effect on other channels not under test.