Ionospheric-induced phase variations between the beginning and the end of a band of 1/2, 1 and 10 LOFAR sub bands (1SB ≃ 0.195 MHz). The dTEC is assumed to be 0.1, 0.3, and 0.5 TECU. These are typical values for distances of a few tens of kilometres. A phase variation larger than ~ 100° creates strong decorrelation. This plot can be used to estimate the maximum amount of averaging (or the maximum band usable to find a single solution) before decorrelating the signal. Coloured bands are the frequency ranges observed by LOFAR.