We study the behaviour of the power spectrum (PS) in the case of fract
al structures. We show that in this case the main observational featur
es of the PS, the large scale flattening and the scaling of the amplit
ude with sample depth, are related to finite size effects, due to the
fractal distribution of the points. Comparing with the recent results
of the PS for the CfA2 we conclude that this catalog is consistent wit
h the fractal description.