Nice job Grant. My EZNEC+V5 (NEC2) indicates that this model is also
resonant on 12MHz and 27Mhz. Since NEC2 does not properly model the short
segments and T elements I am curious what NEC4 shows.
John KK9A
Re: [TowerTalk] 40 Meter MOXON Yagi
from [Grant Saviers] [Permanent Link][Original]
To: Lee <L@w0vt.us>, TowerTalk@contesting.com
Subject: Re: [TowerTalk] 40 Meter MOXON Yagi
From: Grant Saviers <grants2@pacbell.net>
Date: Sun, 5 Feb 2017 11:59:13 -0800
A while ago, there was a request for the W6NL 40m Moxon EZNEC model. I
completed a model of the 120mph design which I had partially done. This is
the scratch build design, and I think the one that Leeson has at his QTH.
I've built two, one for myself and one for K6KR and both have been in use
for 4 years. I also have one in the shed built by K7ZSD.
Here are the modeling results using EZNEC Pro 4 V5.0 for the antenna at 90'
gain 10.7 dbi @ 7.15 MHz at 22 deg
F/B 9.62 db
swr 7.0 1.26
swr 7.15 1.35
swr 7.3 1.9
My 4 years ago measured swr at 90' with an AIM2170 with the coax
calibrated out are
swr 7.0 1.2
swr 7.15 1.35
swr 7.3 1.8
So I conclude that NEC4 can model this Moxon quite accurately. The NEC2
results show swr minimum well below the band but the pattern and gain are
similar at 7.15 MHz.
At 90' NEC4 3d Moxon plot shows a large vertical lobe. At 70' the vertical
lobe is suppressed (TOA 26 deg), so I might lower my tower 20' and
sacrifice about 0.7db of gain. The F/S looks ok. OTA comparisons with my
40m 3L 48' boom at 140' and the Moxon at 90' shows about the same gain
(maybe it is 2db delta) but less noise on the 3L, probably due to the
vertical lobe suppression of the 3L. The Moxon weighs less than 100# and
the 3L 350# and has guyed elements and probably 3x the wind load.
If any modelers want the EZNEC file, contact me off list. Also, error
fixes, optimization results, or better segmentation are of course
interesting as well. My model average gain (free space, no loss) is 1.081
but I haven't spent any effort to optimize segmentation.
Grant KZ1W
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