  We theoretically and experimentally investigated transformations of vortex
beams subjected to sector perturbations in the form of hard-edged aperture. The
transformations of the vortex spectra, the orbital angular momentum, and the
informational entropy of the perturbed beam were studied. We found that
relatively small angular sector perturbations have almost no effect on OAM,
although the informational entropy is rapidly increasing due to the birth of
new optical vortices caused by diffraction by diaphragm edges. At large
perturbation angles, the uncertainty principle between the angle and OAM
involves vortices, with both positive and negative topological charges, so that
the OAM decreases to almost zero, and the entropy increases sharply.
