Homebrew Project 21MHz 4E Yagi Antenna

Months ago I ordered some aluminium in preparation for another antenna project.  Wtih the assistance of John M0UKD the plan was to build a 21 MHz 4E Yagi. The aluminium was ordered from aluminium warehouse, and cost around £100 including delivery.

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The on-line shop provides and delivers lengths of up to 5 meters, and they have a vast selection of grades and lengths available.

The design was by DK7ZB and was chosen because of the short boom length and high gain. The boom is 5 meters, and made from 40mm box split into 2 x 2.5m.  The reflector is 7.2 meters long and director 2 is 6.4 meters long (to give you some scale) You will find all the measurements, VSWR and gain data on Martin’s very extensive website.

The antenna construction involves sections of the elements telescoping into each other, and Martin points out this is a critical part of the design. The aluminium was ordered with this in mind, and while some sections required no adjustment others didnt quite go to plan. We needed to “grind” some of the sections just a little, to ensure they would fit and telescope correctly. This part of the construction required 1 complete grinding disc and around 2 Hrs. work !

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Once each section that required attention was ground down, the elements were mounted on the boom. I used various places to source all the parts but some on-line resources have been linked.

As with any home construction project you always get some unexpected challenges, the first was how to get the elements to lay flat on the plastic formers. The former needs to be mounted to the boom by a nut, and this isnt easy to recess, meaning we had to cut a small hole to locate the nut into the element, allowing the element to lay flat.

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With this type of beam it presents 28Ω (by design) and so requires a coax matching section. This is yet to be constructed, but the final build phase will include this and mounting the driven element.

You can see the progress so far, and further updates and pictures will be posted once tested.

73 Dave M0TAZ
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© 2015 Dave, M0TAZ