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Re: [TowerTalk] Modeling the Moxon

To: k3lr@k3lr.com
Subject: Re: [TowerTalk] Modeling the Moxon
From: Dave Sublette <k4to@arrl.net>
Date: Thu, 27 Jul 2017 12:49:34 -0400
List-post: <mailto:towertalk@contesting.com>
Hi Tim,

thanks for checking in.  I will be calling your guys to inquire about the Yagi 
Mechanical program soon.  I don’t know if you have been following my ramblings, 
but I have plans to make two Moxon 40M yagis out one Telrex 6M46 I have in the 
barn.  I’m in the process of putting my 200 ft rotating Rohn 55 back up.  I 
took it down to move the rotator to 5 ft above ground and will put the tower 
back up to 155.  I plan to put the Moxons at 70 and 140 feet.  I’m looking to 
do some take off angle  analysis because I am on a ridge well above average 
terrain and I think the 140/70 arrangement may work more like a higher array, 
but I don’t know.

73,

Dave, K4TO
> On Jul 27, 2017, at 11:40 AM, Tim Duffy <k3lr@k3lr.com> wrote:
> 
> I have had a stack of two W6NL 40 meter two element Moxon's up for nine
> years. They are converted from Cushcraft XM-240s. Mounted at 185 ft over 120
> ft - both on Ring Rotors.
> 
> The modeled results that W8WWV provides in his summary document (URL
> attached) shows the predicted parameters of the Moxon's at K3LR and they are
> pretty much working as per Greg's analysis.
> 
> http://www.k3lr.com/engineering/
> 
> I continue to be amazed at how good the performance of the W6NL Moxon's is
> when compared to a three high stack of full size four element OWAs that are
> on another tower about 1000 feet away. Sure the big three high stack is
> better - but the Moxon's sure hang tough.
> 
> We are also using a monoband stack switch (mounted at the center of the
> array) to allow selection (and matching) of either Moxon, both in phase or
> both out of phase.
> 
> 73
> Tim K3LR
> 
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> StellarCAT
> Sent: Thursday, July 27, 2017 7:53 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Modeling the Moxon
> 
> 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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