(a) The phase gains of M81* at the eight VLBA stations from fringe-fitting directly on the 7 mm data. Green symbols correspond to the phase in LCP; red symbols to the phase in RCP. (b) The phase gains of M81* at the eight VLBA stations from fringe-fitting directly on the 3.4 mm data. (c) The 3.4 mm phase gains of M81* at seven VLBA stations (NL excluded due to no valid solution) from fringe-fitting on the SFPR-ed data. LA is the reference station in all the gains shown in this figure. (d) The fringe S/N of M81* at 3.4 mm with respect to integration time after phase corrections with SFPR.