Friends in Radio Land -
With the recent postings about magneto-ionic power coupling
for the K1B DXpedition, I have received a number of private
inquiries about the power coupling across the USA. In that
connection, I am listing below the power coupling for a location
in the central part of the USA (Omaha, NE).
At Omaha, the geomagnetic field points 4.7 degrees east of
north and the field lines point down into the earth at an angle of
20.4 degrees from the zenith. At that angle, vertically polarized
waves in the northern direction from a vertical antenna are almost
parallel to the field for a radiation angle of 20 degrees. Hence,
the insertion loss is very small (about 0.1 dB) to the north.
And since the dip angle across the USA varies slowly, insertion
loss at Omaha gives a good idea of the general situation with
vertical antennas.
For a high dipole oriented in the E-W direction, the loss
is much greater, about 17 dB, for propagation to the north and
about 4.5 dB towards the south. For a N-S dipole, the loss for
E-W propagation the loss is about 6.2 dB. Those negative aspects
for horizontal antennas arise when the horizontally polarized
signals have a large component of the electric field that is
perpendicular to the steeply inclined magnetic field lines.
PLEASE NOTE: The losses indicated below are not ABSOLUTE values, just the
additional losses fer a high dipole, whatever the height, due to being
immersed in the geomagnetic field!
Again, a detailed discussion of power coupling is to be found
in the Spring 1999 issue of the Communications Quarterly.
Power Coupling Loss for Omaha, NE
O-Wave, 20 deg rad angle, vertical antenna
Heading Loss Heading Loss
degs E of N (dB) degs E of N (dB)
000 - 015 -0.1 180 - 195 -1.9
015 - 030 -0.1 195 - 210 -1.8
030 - 045 -0.2 210 - 225 -1.8
045 - 060 -0.4 225 - 240 -1.8
060 - 075 -0.6 240 - 255 -1.7
075 - 090 -0.9 255 - 270 -1.5
090 - 105 -1.2 270 - 285 -1.3
105 - 120 -1.4 285 - 300 -1.0
120 - 135 -1.6 300 - 315 -0.7
135 - 150 -1.7 315 - 330 -0.4
150 - 165 -1.7 330 - 345 -0.1
165 - 180 -1.9 345 - 360 -0.1
73,
Bob, NM7M
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