On Mon, 27 Oct 1997 01:36:37 EST k6se@juno.com (Earl W Cunningham)
writes:
>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
Earl and the group:
I have in front of me a EWE design that was sent to me by Floyd, WA2WVL,
a few years ago. It may be of interest inasmuch as the values differ
considerably from Earl's.
For "good soil" 5mm/meter:
Length 50'
Resistor 1285 Ohms
Height 10'
Wire #12
Frequency 1825kHz
Inductance 37uh to tune out reactance at feedpoint
Feed Z 396 Ohms +j7
Elevation Peak 23 deg
Floyd also included a 3 element version with phasings of 0, 135 and 270
degrees. Elements same as above and with 50' seperation making for a
total array length of 250' .
Altho the forward lobe is fairly broad, the F/B over 120 degrees is 50dB
or greater.
The gain is also -22dBi so a preamp is a necessity.
I have not built this antenna yet.
My point here is that there appears to be a lot of discrepancy between
antenna programs. Floyd uses K6STI's AO and this particular run compares
well against NEC-Wires.
Does anyone here have both AO and EZENEC and would be willing to compare?
Perhaps the resolve will require old fashion leg work with some test
equipment.
73 Carl KM1H
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