Calibration of CALLISTO data

The CALLISTO spectrometer is a programmable low-cost heterodyne receiver that can be used, for example, for radio-frequency solar monitoring. Together, various CALLISTO instruments around the world form the e-Callisto network, with each station having the same CALLISTO spectrometer installed in various antenna configurations. Only a few of the stations in the e-Callisto network currently provided calibrated CALLISTO observations, however, limiting the usability of the measurements in, for ex-ample, exact solar flux density estimations. This document describes the essence of how CALLISTO data can be calibrated by using measured power of the cold sky level and an external noise source, using the technical implementation of the calibration system at Aalto University Metsähovi Radio Observatory, Finland.