3D power spectrum for the data shown in Fig. 10, using k²=k²_∥+k²_⊥. This is dominated by k_∥, so the binwidth in k_⊥ does not influence the horizontal position of the limits. The strongest constraints from the 2 and 0.5 MHz filters are shown (square and circle, respectively). Upper limits are 2σ bootstrap errors. Three possible signals are shown. The dashed line is the prediction from Iliev et al. (2008) and the double-dot–dashed line is the same for a cold IGM. The solid line comes from the single-scale bubble model as described in the text for a cold IGM, using k = 2.5/R to show the maximum power at all k. For the two points shown, the bubble diametres which achieve this maximum power are 27 and 7.4 h⁻¹ Mpc, respectively. Only the 0.5-MHz point imposes a limit on the diametre. For a warm IGM case, this signal would be reduced by the same factor as in the two dashed lines.