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Author Topic: dimensions for 3 element Moxon  (Read 878 times)
KU7I
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Posts: 254




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« on: November 03, 2017, 02:38:32 PM »

Looking for assistance in determining the dimensions for a three element Moxon, specifically the director element. One antenna for 20 meters 14.175 mhz and the other is for 17 meters 18.120 mhz. I am familiar with the 2 element Moxon calculators on the internet but am not finding any luck with a 3 element calculator. I want to add a Moxon style director to each antenna. Currently using number 14 stranded for each.

Lane
Ku7i
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N1LO
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« Reply #1 on: November 03, 2017, 04:36:49 PM »

It sounds to me like you are going to be going into Uncharted Territory. With a third element, it will no longer be a moxon rectangle. I think you're going to have to get some modeling software such as EZNEC and give that a try.

With a moxon, the interaction between the reflector and driven element is very strong. I think you will be in for a lot of trial and error to come up with a version that has a director.
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KU7I
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« Reply #2 on: November 03, 2017, 07:22:09 PM »

Thanks Mark.

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WB8VLC
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« Reply #3 on: November 03, 2017, 09:13:46 PM »

I have a 3el 17meter wire moxon that I use which works fine.

Mine uses #12 wire,

the 3 straight long elements, reflector, driver and director are end to end 19.75 feet long.

The end tail wires on each outer end of the three 19.75 feet wires are as follows:

Reflector tails, 3.475 feet long
Driver tails, 3.225 feet long
director tails, 2.95 feet long

the element spacings are as follows, all with respect to the reflector.

Reflector to driver spacing, 7.25 feet.

Reflector to director spacing, 14.575 feet.

So this antenna uses a 14.575 foot boom and it is 19.75 feet wide.

the director tail direction is the same as the driver tail direction toward the reflector and of course the reflector  and driver design follows the standard 2 el Moxon with the added director tails again going in the same direction as the standard Moxon driver.

From these dimensions you can scale from my center Fo of 18.125MHz to your 14.xx MHz Fo if you use a program such as Eznec,

note: I used 4NEC2's optimizer to come up with my design.
« Last Edit: November 03, 2017, 09:20:04 PM by WB8VLC » Logged
KU7I
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« Reply #4 on: November 07, 2017, 05:13:56 AM »

WB8VLC do you have an email I can contact you off line?

Lane
Ku7i
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AC6LA
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« Reply #5 on: November 07, 2017, 09:54:52 PM »

I snooped around with my friend Google and came up with a few more 3-el Moxons in addition to what WB8VLC posted.

YU1QT:  http://www.s55m.com/teh/qt.htm

DX-Antennas:  http://www.dx-antennas.com/M3.htm

Then I created models for all of them, all at a common frequency of 18.125 MHz.  Here's a comparison of Free Space azimuth patterns for the standard 2-el Moxon and three 3-el variants.



Details.



I have a single AutoEZ format model that contains all the dimensions for all the models, available by private email request.  Address shown on my home page or on QRZ.

Michael (Mike?), my apologies if I somehow got your dimensions wrong.

Dan, AC6LA
http://ac6la.com
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WB8VLC
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« Reply #6 on: November 08, 2017, 07:26:27 PM »

Dan,

I trust your results.

The 3el 17 wire moxon wasn't optimized aside from max forward gain using 4nec2,

 I built and installed it in a weekend this summer but now it's down and has been replaced with my 20/15/10 moxon/yagi which went up just this past weekend.

Seeing how narrow the 18 MHz band is it looks like the dx-ant 3el moxon is a better design.

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KU7I
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« Reply #7 on: November 10, 2017, 03:32:25 AM »

Mike WB8VLC and Dan AC6LA,
I scaled down in frequency Mike's original post with his measurements for his 17 meter Moxon to 14.175 mhz assuming an original center freq of 18.120 mhz.

Director tail points towards driven element.  Driven element tail and reflector tail point towards each other.

Total boom length: 18.475 feet.

Width of each element is 25.3075 feet.

Reflector to driver spacing is 9.19 feet.

Reflector to director is 18.475 feet.

Director tips are 3.539 feet.

Driver tips are 3.869 feet.

Reflector tips are 4.695 feet.

Plan to interlace this with 17 meter elements.

Lane
Ku7i

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