[Lowfer] Experimental antenna?

[Lyle Koehler]

Modeling results from NEC-WIRES show that the radiation pattern of the earth
bipole very closely resembles that of a loop in the vertical plane. No big
surprise, since that's probably what it looks like electrically. Maximum
radiation is off the ends of the wires. At very low radiation angles, the
pattern is the classic figure 8, but as you go up in elevation the nulls
start to fill in because of the horizontal radiation component. From what I
understand, LF skywave propagation is primarily at takeoff angles under 8
degrees. At that elevation, the nulls off the sides are about 13 dB down
from the radiation off the ends.

The predicted gain of the bipole at 137 kHz is -22.4 dBi, as compared
to -26.7 dBi for a 15 meter square loop of 1/2 inch copper tubing with the
bottom 10 feet off the ground.

I won't make any guarantees as to the accuracy of the model. Because
NEC-WIRES can't deal with buried wires or with wire segments less than
1/1000th of a wavelength, I simulated the earth bipole with a 1500 foot wire
10 feet above the ground. At each end, there is a vertical wire going down
to a large ground pad, consisting of twelve 100-foot radials with a skirt
wire, 1 foot above ground. The ground characteristics were the defaults for
NEC-WIRES, with a dielectric constant of 13 and a conductivity of 5 mS/m. I
expect that the actual gain figure for the earth bipole depends strongly on
the ground characteristics, and whether you're using a deeply buried ground
connection. However, the pattern is likely to stay pretty much the same as
long as the antenna dimensions are appreciably shorter than a wavelength.

Lyle, K0LR