More on "Bang" per kW
Recently, I posted the results of some calculations showing how
the earth's magnetic field affects DXing with vertical antennas.
Sites were used, areas of strong DX activity, on six continents.
The results were favorable, as expected, because of the fact that
vertical antennas do not represent a significant mis-match with
the geomagnetic field, largely vertical on the continents.
Thus, for a kW of radiated power, the fractional power transfer
to the ionosphere by vertical antennas ranged from 0.41 to 0.98,
with an average of .765 for all the sites. It should be noted the
lowest power transfer was for Brazil where the field is more
horizintal than vertical, giving a much greater mis-match with a
vertical antenna.
I did receive some inquiries about other sites, e.g., New Zealand
as compared to Australia, and horizontal antennas, e.g., dipoles
and Marconi L-antennas as compared to vertical antennas. It
should be noted horizontally polarized antennas present a problem
for calculations because on 160 meters they must remain fixed in
position and the questions of orientation and radiation pattern
then come up. In order to give at least some indication of their
potential use in DXing, two orientations for dipoles were chosen,
having N-S and E-W broadside radiation directions.
The results of the calculations were disappointing, as expected,
because of the mis-match between horizontally polarized signals
and the largely vertical magnetic field. That was particularly
true for a dipole radiating broadside in the N-S directions,
i.e., with the antenna element aligned E-W. For that case, the
fractional power transfer to the ionosphere by a E-W dipole ranged
from 0.005 to 0.42, with an average of .115 for all the sites. As
expected, the highest power transfers were for Brazil, with its
near-horizontal field.
The fractional power transfer to the ionosphere by a dipole
with its element oriented N-S was better, ranging from .005 to
.56, with an average of .185 for all the sites. Again, the
highest power transfers were for Brazil.
>From these calculations, it is clear the vertical is the antenna
of choice for 160 meters DXing. If a horizontal antenna must be
used in the USA, its element should be aligned N-S as the
polarization-field mis-match is less severe when the aspect the
field presents to horizontally polarized waves is broadside rather
than head-on.
Those interested in the details should contact me directly.
73,
Bob, NM7M
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