  Generation of Alfv\'en and slow magneto-acoustic waves in weakly ionized
atmospheres by excitation of the charges-only component of the two fluid
(charges and neutrals) plasma is shown to be more or less efficient depending
on the energy fraction initially allocated to the three stationary "flow
differential" modes which characterize the inter-species drift. This is
explained via detailed analysis of the full ten-dimensional spectral
description of two-fluid linear magnetohydrodynamics. Excitation via the
velocity of the charges only is found to be very inefficient, in accord with
previous results, whilst excitation via the magnetic field perturbation alone
is highly efficient. All ten eigenvalues and eigenvectors are presented
analytically in the high collision frequency regime.
