Phase solutions in radians for four different stations (CS302, RS106, RS508, and RS509) plotted as a function of observing time (x-axis) and frequency (y-axis). Colour goes from −π (blue) to +π (red). All phases are referenced to station CS002, at the array centre. First panel: phase solutions for the XX element of a diagonal Jones matrix obtained at the beginning of the calibration. Those solutions encode all the systematic effects affecting LOFAR LBA phases. Second panel: same as above but after the subtraction of the clock systematic effect, only the ionosphere is visible. Third panel: same as the first panel, but after the subtraction of the ionospheric systematic effect, only the clock is visible (CS302 has the same clock of the reference). Bottom panel: same as above but solving after the subtraction of all recovered systematic effects, i.e. at the end of the calibration pipeline. The uniformity of the plots shows we are able to remove systematic effects with high accuracy. The HBA equivalent is shown in Fig. A.1.