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Author Topic: Need feedback on Moxon Antenna design  (Read 682 times)
KJ6TSX
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Posts: 116




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« on: January 11, 2014, 09:14:19 PM »

I have fumbled my way through designing a Vertical Moxon antenna with three reflectors, a driven element and a director. It appears to have over 1 DBI over a plain Moxon antenna at 18 feet to the bottom of the antenna. The antenna is designed for the 10 meter band. I would like to get some feedback on my design and some advice as were to locate the coax balun. Previously I have had the balun located at the feed point with the coax then running at right angles from the driven element to behind the reflector, then down to the transmitter, would it be better to locate the balun behind the reflector or on the mast below the antenna? It might be easier to visualize what I am asking by looking at this link. The link also has the 4nec2 radiation patterns, SWR line charts and a drawing of the antenna https://dl.dropboxusercontent.com/u/105294183/Moxon%20with%20multiple%20relectors.pdf

This link is to the4nec2 input file https://dl.dropboxusercontent.com/u/105294183/Moxon%2027.5%202reflector-6%2BDir-1.nec

Any feedback will be greatly appreciated
Thanks
KJ6TSX
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W5WSS
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Posts: 1745




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« Reply #1 on: January 13, 2014, 08:42:53 AM »

The mast below the antenna. and best directly beneath and at the feed point.

The treatment is the same as with a vertical and a choke balun. and run the feed line routed straight down perpendicular to the antenna. downwards along the vertical mast.

The vertically oriented Moxon (driven element in this specific case) incorporates a split gap so in essence is an balanced set of conductive wires.
The Good design choke is needed because 50 ohm coaxial feed line is electrically the opposite so there exists a balance to unbalanced transition to be remedied with the use of a1:1 current balun/choke interchangeable.
(This will work fine assuming a 50 ohm antenna impedance) the antenna feed line is the proper Characteristic impedance required by the antenna system. (I am skeptical honestly, because when you add a 3 reflector series and a director the antenna RR is probably not 50 ohms but it can be designed to be 50 ohms) but regardless with the balun the potential equilibrium is restored and the match can be tuned.

Have fun 73
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W5WSS
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Posts: 1745




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« Reply #2 on: January 13, 2014, 08:46:09 AM »

Also ideally, the mast should be non conductive until it clears the base of the antenna then can be metallic.
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KJ6TSX
Member

Posts: 116




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« Reply #3 on: January 13, 2014, 02:18:20 PM »

Thanks for the reply.
Do you have any suggestions for a good 1:1 current balun?
You suggested running the coax down the mast between the driven element and the reflector?Huh? Would it be better to run it behind the reflector in other words horizontally from the feed point to behind the reflector then down??
Some talk on other threads Suggest 10 DBI on a moxon I had trouble getting 6+
Thanks
George
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