2m Yagi for portable SOTA

Building a portable Yagi Uda antenna was actually THE reason why I got my 3d printer. My first project was a fail. Since I wanted an antenna design that uses elements that can be split in half for easier packing and carrying around.
My first try was with aluminum rods and drilled holes. I cut a thread in them and used a threaded rod to connect the elements. It did not work out as I dont have a drillpress and can’t cut threads 100% perpendicular by hand. So the project laid around until recently.

DK7ZB design

I got the dimensions from DK7ZB’s website. I chose the 4-El.-50Ohm (0,76m) version. First I wanted to make the 28Ohm version, but in the end I went for the 50Ohms. I will make another 2m modular Yagi with a larger boom some time later on and then probably try out the 28Ohms. 

The problem with the elements

The challenge was how to connect the elements if they are separated in two halves. Also, how to connect the radiating elements temporary for use. I came up with a quite odd solution. For the radiators I took two screws that press on to the radiators and are hold together by the casing for the choke. 
The directors and reflector is hold togehter by a clamp that is using an aluminum plate to couple the two halves. I am not an expert and I honestly don’t know if such coupling somehow affects the element as one piece and its performance as a director. I was not able to get any copper tape. I assume, when using a copper tape it would be much better.
If you choose to take the same approach, make sure you file down the eloxated part on the aluminum.

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Measurements

copied from https://www.qsl.net/dk7zb

Diameter	Reflector	Radiator	Director 1	Director 2
6mm	1040mm	1028mm	960mm	891mm
8mm	1034mm	1032mm	952mm	874mm
10mm	1030mm	1030mm	944mm	864mm

Elementpositions

Reflector	Radiator	Director 1	Director 2
0	250	345	755

When using those numbers, I took 0.5cm less for each radiator, as there is a 1cm spacer in the clamp. 

SWR and the feeder line

While doing my first SWR measurements I was going nuts. I realized that it really matters how you layout your feeder coax on the pole and the boom and that you should take great care about that. Since I had no room for the feeder to go forward on the boom, rather backwards, I had a problem. 
Using a 90° BNC adapter I could solve that issue temporarily. I got down to 1.4 SWR. I bet it would be better if I could just get this BNC plug on the opposite side of the choke. 

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What you need

• 15x15x100 aluminum square boom
• 6mm hollow aluminum rods
• aluminum plate to connect the elementhalves together OR copper tape
• 9 x M5 wingnuts
• 2 x M5 x 50 hex screws
• 7 x M5 x 30 hex screws
• 4 x M5 x 10 or 15 hex screws
• 5 x M5 nuts
• 10 x M5 washer
• 2 x M4 x 10 hex screws
• 2 x M4 smaller washers
• 2 x M4 nuts
• 6 x M2.5 x 15 SPAX screws
• ~40cm RG174 coax
• BNC socket
• 3 x car cable clamps
• ~10cm wire

Assembly and 3d printing

When you start to print the pieces, make sure you decide which method you want to use for connecting the elements together. I made two versions of the clamps (the pieces that are mounted to the boom). Clamp round and square. The clamps are best printed vertically, so the square which holds the boom is printed without supports. It’s a pretty tight fit, so you may need to use a plastic hammer and a lighter to slide them on the boom. 
The opening on the side of the clamp is used to slide the clamp into the right spot on the boom. You may reuse it for other Yagi designs, since no holes are needed. The screws on the bottom of the clamp are used to fix it in place. Make sure you dont overdo it, your plastic may break.

The coil for the choke is wound outside the box and then glued into the casing with hotglue.

IMPORTANT: when printing the screw for the telescopic clamp, please scale X and Y to 90%, leave Z (height) on 100%!

If you have any questions, leave a comment.

You can download the STLs on my Thingiverse account 

Download at Thingiverse

Have fun with your portable Yagi!
73,
9A5ALX