Tuesday, June 21, 2011

20 Meter Vertical Moxon

20 Meter Vertical Moxon

Thanks to this site and Pete Mills in particular I decided to build a Moxon to take on our trips to the Scottish Islands. Wire dimensions were as Pete's EZNEC model. Mark 1 used a couple of fishing pole as supports but the bent far too much in the wind so I decided to engineer a more substantial arrangement that is easier to put up.

The beam is supported by two cross arms mounted to a push up GRP mast and the pictures below show the mounting arrangements. To eliminate as much metal as possible from within the beam I used a form of GRP plate called TUFNOL to fabricate the mountings, with hydraulic pipe clamps used for the tube clamps. These are also plastic only leaving two bolts and a plate that are metallic.

At the end of the cross arms I bolted in eye bolts so that the wire element can be quickly clipped into place. The wire is supported at each corner by a dog bone insulator with a cable tie either side of it to hold the insulator in place while the antenna is being erected. The dog bones are attached to a short length of Kevlar line with a snap link at the far end.

The push up mast I use was supplied without any provision for guying so again I made some guying rings out of TUFNOL. These are used with Kevlar guys and one up the whole thing is very stable and has stood up to some high winds with no problem.

This is the antenna erected and you can clearly see the upper cross arm. The lower one isn't as visible but it's the same idea. This arrangement works much better than I imagined - it keeps the wire in tension in all dimensions and can be put up by one person easily. It also packs up into a convenient size as the cross arms are each 3 sections of 1 metre long.

The sections for the cross arms came from a company called spiderbeam http://www.spiderbeam.net and I can recommend their stuff (no association).

The antenna worked exceptionally well adjacent to the ocean and as a result we managed over 4500 QSO's in 6 days with Japan and Asia contacts coming very easily with our 100W.

Les Moxon, G6XN originally designed the Moxon Rectangle based upon a design by Fred Caton, VK2ABQ. L.B. Cebik, W4RNL optimized a wire version of the Moxon. The Moxon can be visualized as a 2-element yagi with the element tips bent towards one another. The tips are separated by an insulator creating a gap which is mostly responsible for the directive pattern unique to the Moxon.


The Moxon is a directional antenna system that is gaining in popularity because it offers three very distinct advantages over a typical two element Yagi:

  • Small in physical size. The Moxon can be built using a very lightweight structure and wire elements, which will fit into a footprint about two thirds the area required for a conventional beam. You can see by the measurements above that a 20 meter Moxon is only 25 by 9 feet. Being a very light structure, typically made from wire and lightweight spreaders, it can easily be mast mounted on a lightweight pole, hoisted up in a tree from an overhanging branch, or turned vertically and ground mounted! As such it also makes an excellent field antenna.
  • Outstanding front to back ratio. The Moxon's front-to-back ratio models at greater than 30dB! Moreover, close-gap coupling enables the Moxon's enhanced performance to be realized at lower elevation heights of only 1/2 wavelength. As seen below, the Moxon exhibits a broad forward area combined with superior front to back.


  • The Moxon is a 50 ohm antenna, generating a near perfect 1:1 swr without requiring any additional matching devices. It is also quite broadbanded allowing for effective full band coverage.

The Moxon antenna can provide hams with an excellent antenna system that is easy to homebrew and usually does not require any adjustment if made according to the dimensions specified by software that is available on this website. A typical Moxon rectangle can be built in a few hours, using X or H type of spreaders made from bamboo, fiberglass, pvc or a variety of other materials.

Building the Moxon is fairly easy and lends itself to imagination. No two Moxon's are identical save the dimensions of the elements and spacings. If you view the various antennas in the What's New section on the homepage, you'll see what we mean. You can also view a variety of different hubs and designs here.

Since the Moxon is a 50 ohm antenna, you may or may not want to use a 1:1 balun. It's your choice. If you are planning on running any power, you might want to install a balun at the feedpoint. If you're not running any power, then feed the antenna directly from the coax (see Balun Notes below).

Once you've decided on what type of wire to use, and have used the Moxon Software to calculate the dimensions according to your band, you're ready to start constructing your Moxon. So, let's build one. Shown below are the dimensions for the 20 meter band.:

Here we've started the moxgen software, used 14.175 as center frequency, selected our #12AWG wire and hit calculate. The results are shown in inches, but you could have selected other units. You can even generate an eznec or nec antenna model (shown elsewhere on this website). So, looking at the diagram, we can see that the overall antenna will be 303.47 inches, or 25 feet long and just over 9 feet wide.


Sample Construction materials:

1 1/4 Inch conduit (for pole brackets)

U bolts/pipe hangers


4" x 1/4 plate (Mast bracket)

1/4 or 5/16 bolt

1/4 or 5/16 nylock nuts

16 gauge tinned wire

16' Crappie Pole spreaders

The pole bracket assembly was made by bending and flattening the conduit and inserting fiberglass crappie fishing poles as antenna spreaders into the open end..

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