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Re: [TowerTalk] 40 Meter MOXON Yagi

To: TowerTalk@contesting.com
Subject: Re: [TowerTalk] 40 Meter MOXON Yagi
From: Alfredo via TowerTalk <towertalk@contesting.com>
Reply-to: Alfredo <wp3c@aol.com>
Date: Sun, 05 Feb 2017 14:22:47 -0600
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
Hi everyone 
Is posible make this with Force12 EF-240X?

Alfredo Velez WP3C/NP4DX
e-mail: mailto:wp3c@aol.com
Web: http://wp3c73.wixsite.com/wp3c
Sent from my T-Mobile 4G LTE Device
-------- Original message --------From: Grant Saviers <grants2@pacbell.net> 
Date: 2/5/17  1:59 PM  (GMT-06:00) To: Lee <L@w0vt.us>, 
TowerTalk@contesting.com Subject: Re: [TowerTalk] 40 Meter MOXON Yagi 
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


On 2/5/2017 8:55 AM, Lee wrote:
> I might add, I suspect one could adjust the matching point to 50 ohms 
> bye using a delta connection running out on both sides from the center 
> of the driven element provided the center point would give you 
> something less then 50 ohms.  Just seems there should be a better 
> MOXON program then MOXON Utility.  I'm also thinking one could 
> increase bandwidth bye wrapping the fiberglass tubing with aluminum 
> foil.  Fiberglass intrigues me as it is lighter then aluminum tubing.  
> (Wrapping it before the helical loading coils.)
>
> Lee, w0vt
>
>
> On 2/5/2017 10:33 AM, Lee wrote:
>> Some time ago I decided I wanted to build a full size 40 meter Moxon 
>> Yagi beam.  It never happened. Right now I've gotten Cold Feet to the 
>> project.  I'm beginning to think the beam would be just too heavy for 
>> my situation.  I'm now considering building a 40 meter Mini MOXON 
>> beam as built by W7XA.  This rendition uses fiberglass tubing instead 
>> of aluminum tubing and is inductively loaded making it close to a 26 
>> foot x 16 foot rectangle.  Has anyone on here built one?  I'd like to 
>> hear from you if you indeed have one up and running.  Since 
>> fiberglass tubing is shipped in 8 foot lengths, the two elements 
>> would be made up of 4 eight foot lengths.  The design has an element 
>> length of 26 feet.  That means I'd have to discard 3 foot off two 
>> pieces.  I looked at the MOXGEN UTILITY Software and for 7.1 Mhz, the 
>> program shows you all the other beam dimensions. They were as W7XA 
>> described except for he shortened the two elements and made up for it 
>> with loading coils.  What I don't know is if I make the two elements 
>> longer to make use of the full fiberglass tubing and then if I reduce 
>> the size of the inductors to maintain resonance, will I upset the 
>> feed point impedance?  I'm thinking this will be the case.  But, by 
>> altering the length will I be able to find a 1:1 SWR at 7.1 Mhz ?  
>> The bottom line to all this is, will I screw up the feed point 
>> impedance by  making the elements longer and have smaller loading 
>> coils?  Then too, I'm not sure W7XA actually saw 50 ohms at his feed 
>> point with his design in the first place. Looking at the MOXGEN 
>> software, it does not appear you can alter element spacing with it's 
>> program.  It just gives you all the dimensions without loading coils 
>> for a specific frequency.  (The only thing I see you can do with the 
>> program is put in the desired frequency and you give the element 
>> diameter.  Also, what happens to the impedance if I use a longer boom 
>> like 20 foot instead of 16 foot?  I think the impedance would then 
>> change too.  The MOXGEN software doesn't allow you to pick different 
>> length booms. Anyone on here brighter then me on this subject?  Is 
>> there a better software program for designing a Moxon Yagi beam then 
>> MOXGEN UTILITY?
>>
>> Lee, w0vt
>> _______________________________________________
>>
>>
>>
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