  We report the one-electron spectrum and eigenstates of infinite achiral and
chiral $(2m,m)$ carbon nanotubes found by using the analytic solution to the
Schr\"odinger equation for the tight-binding H\"uckel-type Hamiltonian. With
the help of matching the wave functions on the interfaces between the regions,
where electrons have different site energies, we find and compare the
transmission coefficients for zigzag, armchair and chiral nanotubes subjected
to the action of an applied step-like potential. The correspondence between the
nanotube band structure and the energy dependence of the transmission
coefficient is demonstrated. It is shown that the $(2m,m)$ nanotubes with a
medium chiral angle reveal intermediate transport properties as compared with
the achiral armchair, and zigzag nanotubes.
