  A reciprocal space formulation of the Cluster Variation is used in order to
extract effective pair interactions in alloys from experimental short-range
order diffuse intensities. The method is applied to the analysis of the short
range order contribution to the neutron diffuse scattering of a $Fe-19.5 {\%}
Al$ single crystal. A detailed comparison with real space methods is carried
out for three different levels of approximations. For the highest level of
approximation used in this study, effective pair interactions up to fifth
neighbors are obtained.
