Dear Steve and all,
In my e-mail to Steve, VK6VZ, I specified a variation of the Ewe which
required only one 10' support. For "very poor" soil, I said the wire had
to be 20' long and supported in the middle with a 10' pole, with both
ends of the wire running to ground level. I didn't mean that to be a
joke -- it was a blunder on my part. As Bob, K6ZZ pointed out during a
respite in the contest, a 20' wire would have both ends come straight
down from the 10' level (and would look like a folded unipole).
What I meant to say was "a wire, supported at its center, which is long
enough to reach the ground 10' horizontally in both directions from the
center support pole." Such a wire would have to be about 28' 3-1/2"
long, not 20 feet.
I made the same blunder on the Ewes for "poor" soil and for "good" soil.
Their corrected wire lengths are 32' 10" (poor soil) and 36' 1" (good
soil), supported at the center of the wire by a 10' post.
The obvious attraction of my variation of the Ewe is that it requires
only one 10' support and very little real estate. It turns out that, for
best front-to-back ratio when using a 10' support, there are different
optimum sizes and termination resistances for different types of soil
conditions. I optimized Ewes of this variety for "very poor", "poor",
"good", and "very good" soil conditions. All are supported in the center
of the wire at 10', all are optimized for best F/B ratio (better than
45dB), all are constructed of #14 copper wire and all are designed for
1.83 mHz. These are the results:
"VERY POOR" (1 mmho/meter) Soil:
Wire length = 26' 11" (ground level at +/- 9' from the center
support)
Termination resistor = 4200 ohms
It takes about 114uH at the feedline end of this Ewe to resonate it at
1.830 mHz.
-------------------------------------------------------
"POOR" (2 mmhos/meter) Soil:
Wire length = 32' 10" (ground level at +/- 13' from the center
support)
Termination resistor = 3425 ohms
Inductance to resonate the wire at 1.83 mHz = 92uH
-------------------------------------------------------
"GOOD" (5 mmhos/meter) Soil:
Wire length = 35' 3" (ground level at +/- 14' 6" from the center
support)
Termination resistor = 2100 ohms
Inductance to resonate the wire at 1.83 mHz = 72uH
-------------------------------------------------------
"VERY GOOD" (30.3 mmhos/meter) Soil:
Wire length = 45' 7" (ground level at +/- 20' 6" from the center
support)
Termination resistor = 1100 ohms
Inductance to resonate the wire at 1.83 mHz = 37uH
--------------------------------------------------------
Modeling shows that any other length of wire supported at 10' at its
center will not perform as well as the values given here. All have a
cardioid pattern with a deep null at the rear.
My apologies to all for the blunders.
73, de Earl, K6SE
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