My model is the W6NL scratch build 40m Moxon. I obtained different
results using EZNEC Pro4 with the bottom at 70' and top at 140' the peak
gain of either alone is 10.5dbi and 11.0dbi respectively over average
real ground. As a stack the gain is 13.2dbi or 2.2db higher than the
140' alone. This is in line with other stack modeling I've done and in
the range of many published results re stacking gains, practical and
theoretical.
This model's AGT is 1.024 alone or stacked.
My QTH real-time A/B comparison is the Moxon at 91' vs a full size 3L
48' boom at 140'. The 3L most always wins, lower angle, lower noise
with better F/S and F/B. Not a fair comparison by any means.
Regarding stacking separation, for two high stacks in the modeling I've
done, near 1/2 wl the gain is pretty much asymptotic to its max value.
Grant KZ1W
On 7/27/2017 4:53 AM, StellarCAT wrote:
Dave's original statement was "can someone model 2 40 meter yagis
stacked?" .... at the time the discussion was about stacks - then got
in to the relative performance of 40 meter stacks ... my intent was/is
to do just that ... 2 x 2 element yagis will serve the purpose. If
modeling the interaction of the 40 on say a 15 (it won't interact
noticeably with a 20) then I can attempt a Moxon. Note I have modeled
a Moxon before with results that seem correct ...using NEC2.
Regarding 40 meter stacks ... when I model 2 x 2 element yagis at
140/70 the increase in gain is only about 1.4db ... which was my
original point that there isn't a great deal gained from stacking on
40 meters other than the change in angle (which again the lowest one
will seldom be the better choice over the stack) and if available
having the ability to go 2 different directions... extending that to 2
4 element antennas the increase in gain is even less - less than 1 db.
My original comment was you need to get 40's up higher and further
apart to start to get a bit more gain increase. (that stated even with
20's stacked the increase in gain when stacked "properly" is 'only'
about 2.4 db or so).
Gary
-----Original Message----- From: Joe Subich, W4TV
Sent: Wednesday, July 26, 2017 8:00 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Modeling the Moxon
If you intend to model a Moxon, particularly the Leeson Moxon, you will
need software that uses the NEC4 engine.
NEC2, commonly used in amateur software because it is free, does not
handle right angle connections and tapered elements correctly.
Numerical corrections have been developed for the taper issues
(primarily by Leeson) but NEC2 still does not handle elements that
are not parallel very well.
73,
... Joe, W4TV
On 7/26/2017 6:28 PM, Dave Sublette wrote:
I have spent a fair amount of time reading a few of the Moxon
construction articles about the modified Moxon for 40 meters. I have
a spare 6 element 20 meter Telrex monobander for 20 meters in my
barn. Doing some scratching on paper, it looks like I could build
two, two element Moxons for 40 using the material in that yagi. I
would need to buy the tubing necessary to build the Tee sections on
the end.
Since all of the element diameters and taper schedules would be
different, I should model it. I have the Antenna Model Software
package. I haven’t used it much. I haven’t modeled antennas in over
15 years. I used to use K6STI software when I did and I loved it.
Some of the articles I have read say good things about the Antenna
Model program. I am wondering if that would be good enough to use on
the Moxon.
Now I know the Moxon doesn’t model well. The W6NL version is the
standard and the best advice is to build it like that. But I have
all this beautiful aluminum that I don’t want to waste. Plus, the 3
1/2 inch boom on the T-rex is really stout enough to handle this
antenna. At least one article says they wish they had used a larger
boom diameter.
I suppose a good plan would be to model the W6NL and then my version
on the same software and adjust my version until the results matched
those obtained with the W6NL. The question is .. Is the Antenna
Model package adequate for the job?
A really good answer would be that someone has already modeled the
W6NL on Antenna Model and would share the file with me. :-)
Thanks,
Dave, K4TO
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