The issue of horizontal vs. vertical polarization for transmit
antennas often arises in 160 mtr discussions.
Davies' book, Ionospheric Radio Waves, 1969, provides some
interesting info.
For low angle propagation, other things being equal, the following
appears to be the case:
For QTH's where the magnetic field dip angle is high, at least 45
degrees and especially over 60 degrees:
(All North America dip angle is >60, all Europe >45 and No. Eu. >60,
So. Africa >60, NZ >60, most Australia >45, So. Aust. >60.)
Vertical polarization is best for all directions of propagation.
This is because vertical polarization will excite mainly the ordinary
wave, while horizontal polarization excites mainly the extraordinary
wave in the ionosphere. At 1.8 MHz the extraordinary wave is highly
absorbed (not true at higher frequencies).
For QTH's near the magnetic equator, the situation is different.
(All So. America dip angle is <45, most SA < 30, Indonesia aprox. 0.)
For these QTH's, for East-West propagation at low angles, horizontal
polarization is best. Again, horizontal polarization excites the
less absorbed ordinary wave. For North-South propagation from these
QTH's, the ideal polarization would be circular (in the correct
rotation direction), otherwise either horizontal or vertical
polarization will each excite the ordinary wave (at 3 db loss).
Thus, overall, horizontal polarization would appear to be the
better choice for these QTH's. A low angle horizontal radiator is
needed, e.g., a W8JK array, or full wave dipole, or rhombic.
For QTH's with dip angle of about 45 degree (e.g., Japan, extreme
No. Australia), either horizontal or vertical polarization would seem
to be OK.
So, a dipole in Norway probably won't work well at any height,
while it might do well in No. Australia or Indonesia. A rhombic in
So. Africa might not work well, but could be great from some
Pacific islands.
Incidentally, Davies also mentions a bit about non-reciprocity in
propagation related to polarization. He gives examples where
polarization changes differently going in the two directions, such
that going one way (say to the East) the polarization changes to
match the polarization at the East QTH antenna, while going the other
way (to the West) the polarization ends up opposite to that at the
West QTH antenna, so "one-way propagation". In this case, the West
station needs to listen on a rx antenna of different polarization
from his optimum TX antenna.
Please, anyone who is more of an expert in these matters, correct any
errors in the above.
73, Rod VE7FPT
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