The results of a special experiment to study the statistics of short-wave signals reflected from the ionosphere during F-spread conducted in the first half of 1994 at the proving ground of the Scientific-Research Radio-Physics Institute at Zimenki of the Nizhny Novgorod region are presented. The dependence of the index of amplitude fluctuations on the reception bandwidth was studied. The experiment results are compared with existing theoretical concepts of the origin of F-spread. The experiment favors the hypothesis that middle-latitude F-spread is result of the multiple-ray nature of short-wave signals reflected from the large-scale quasi-regular inhomogeneous structure of the ionosphere.