  We show that the public experiment held in Venice by F. Tamburini et al and
reported in (2012 New J. Phys. 14 033001) can be regarded as a particular
implementation of Multiple-Input Multiple-Output (MIMO) communications, hence
bringing no advantages with respect to known techniques. Moreover, we explain
that the use of a 'vortex' mode (orbital angular momentum OAM l = 1) at one of
the transmit antennas is not necessary to encode different channels since only
different patterns -or similarly different pointing angles- of the transmit
antennas are required. Finally, we identify why this MIMO transmission allowed
decoding of two signals despite being line-of-sight. This is due to the large
separation between the receiving antennas, which places the transmit antennas
in the near-field Fresnel region of the receiving 'array'. This strongly limits
the application of this technique in practice, since, for a fixed separation
between receiving antennas, the detectable signal power from any additional
vortex mode decays at least as 1/r^4.
