Time behaviour of noise spectra on selected periods for radiometers 18M (70 GHz, left), 24S (44 GHz, centre), and 28M (30 GHz, right). White noise and 1 /f noise are constant within 0.5% until OD 326, after which degradation of the sorption cooler and the switchover to the redundant cooler introduce higher thermal noise at the lowest frequencies. Vertical lines mark the frequencies corresponding to the spin period (1 / 60 Hz) and the baseline used in the mapmaking (1 Hz).