Multiband light curves of AO 0235|$+$|164 in 1997–2023. Four epochs chosen for analysis are depicted by the straight vertical lines. The historically quiet state between 2009 November and 2014 March is indicated by the grey area and shown in detail in Fig. 3. The blue area at 2 and 5 GHz is the time interval of the daily observations (see the description of RATAN-600 observations and Fig. 6).