[TowerTalk] Beta match adjustment

[Tim Duffy K3LR]

HI Kevin,

I built two W6NL Moxon's. I have had them in the air for several years.
They work perfectly. Nothing changes when the wind blows.

The W6NL Moxon antenna has superior performance characteristics when
compared to the Cushcraft 2 ele 40 (which I used before the W6NL design).

I do constant comparisons between the W6NL two element antennas (in a stack)
and full size 4 ele OWA antennas (stacked). There are no surprises or free
lunches. The larger antennas have more gain and more front to back, as you
would expect.

However, for a 2 element Yagi - on 40 meters, with a 22 ft boom - the W6NL
Moxon's forward gain, F/B pattern, feedpoint simplicity and wide VSWR
bandwidth - the combination is tough to beat.

73,
Tim K3LR 

http://www.k3lr.com


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Kevin Normoyle
Sent: Sunday, July 18, 2010 4:19 AM
To: Tower Talk List
Subject: Re: [TowerTalk] Beta match adjustment

K3LR recommended the W6NL moxons.

Yeah I had looked at the various W6NL variations, and decided against them.

In the end, I'm not convinced the extra aluminum is worth it, compared 
to a regular moxon made of aluminum tubing? (it is more aluminum, right?)
I think it should have been compared to another moxon, not to a 2 
element or 3 element yagi?

Also, since the tip coupling is critical, I would think the unconnected 
tips would cause variance when they move?

That's why I set to build just a regular moxon initially.

I tried using W6NL's nec model. Using 4NEC2, it seemed to me to be tuned 
for lower frequency?
Supposedly it's dialed in though, so something must be wrong for me..
I'd be curious if anyone can run W6NL's  in EZNEC and do a freq sweep. 
(files below)

I think that's related to what happened with my 40M simulation. I was 
optimized in too high in frequency.

So somehow, I'm missing something in my simulation.

Here are my .nec that ended up being high in frequency (my bent tip with 
hairpin sim). I then did one optimized for lower frequency (6.9Mhz)
You can see the gain/fb/swr bandwidth though.
.nec files.
  I'm a newcomer to simulating, and maybe someone out there can give me 
feedback.
It's got the right wire seg diameters for the taper I used.

download from here:
https://sites.google.com/site/knormoyle/
the first "built_5_16_bent2l_40m_233boom.nec" was my sim I built from 
but adjusted.
the elements are full length, bent tips, antenna at 55' (yeah, i had an 
old wt-51 laying around too I put up..)

W6NL provided an AO file for his antenna here
http://www.kkn.net/dayton2004/

I converted it to NEC and it's my site above also. called "W6NL40.nec"

I'd be interested in whether people simulate that and whether it appears 
low in frequency or ?? (I see 6.8mhz center point) for the w6nl40.nec at 
my site. I even tried adding a boom to see if there were some effects I 
wasn't modeling, but couldn't get it better.
Maybe I need NEC-4 instead of NEC-2?

-kevin AD6Z



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