Sunday, October 24, 2021

5 band quad HF antenna design, building and ideas (part 1)

 Recently I spoke a few stations from around the world on 10m which were reasonable strong. All those stations were transmitting with 2 or 3 element (multiband) quad antennas. And for shure these stations were way stronger then any other on the band at that moment. If you ask antenna experts they all say there is no difference between a quad and yagi radiation pattern and f/b ratio in the end. With other words, you can do the same thing with a yagi as a quad. But I'm not really a HAM that does rely on theoretics, I want to see what something does in the real world. Being this something is an antenna or anything else.

This post is primarely for myself to write down some ideas (and receive some ideas in the comments if you as reader has them). It is no secret I want to build a 5 band HF quad antenna for quite a while. But it brings some technical design challenges and takes time. In my last musing about antennas earlier this year I wrote about the only user of the particulair DK7ZB quad design I know; G0VXE Dave definitely tuned the reflectors on his antenna and that seems to be the biggest challenge. However, the f/b ratio will be about 10-15dB which is not to be compared with 25-30dB a yagi will have. I expect in practice it will show about 1-1,5 S-point in comparisation between front and back. However, it seems side rejection will be excellent.

This post is about design ideas I found on the internet. Ideas that are simple but can be forgotten just as simple.

My idea is to make my 2,85m boom from the green militairy glasfiber poles I used for my 80m horizontal loop in the past. To mount the glasfiber telescopic tubing on the boom I found this idea made from alu corner profile, I made one prototype:


Since I use cheap glasfiber fishing rods for the prototype antenna I use alu tubing to reinforce the first 50cm of the rods since I think this is the part of the rod with most of the stress.


Made two prototypes. I will wrap the rods with black tape against UV and weather influences. The rods are quite strong. To test I grabbed them at the thin top and hold it horizontally in the air. 


The full weight is now at the weakest part. It does bend but doesn't break. I feel confident the rods are holding everything in the air at high windloads. The rods are 4,1m long.


Above the alu tubes I use to reinforce the rods. They are wrapped with tape to better fit in the rods. I also ordered a spool of 2mm alu wire. I really thought about insulated copper wire but there is a big disavantage, the weight is substancial higher. Also I would have to recalculate the design published on the DK7ZB website

To get an idea of the size I put some rods in angle configuration to simulate one side of the quad.




It is the idea to mount the quad in the mast the square way and not in diamant shape like G0VXE did. The advantage is that the sides are a lot shorter. Approx. 2,75m. Making total width of the antenna 5,5m which is managable in my garden.


Not to forget the details. I learned this from another antenna experimenter on youtube. It is definitely the best way to prevent the telescopic rods to get loose and slide into each other. This can happen when force is applied by mounting the wires. Count on big forces in a storm. I don't know how these rods will behave when temperature will be freezing in winter?

I found this idea to mount the wires on the poles. The tube used seems to be UV resistant airbrake hose. 


8 comments:

  1. WOW! Is that your back garden Bas?? Wish I had that much space, lol. Good luck with this project - I will follow with interest.

    73, Tom.
    www.M7MCQ.com

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    1. Only part of the garden Tom. I got about 20mx20m space in the backyard. Use to have a 80m horizontal loop around it in the winter. But my XYL will not allow it anymore. 73, Bas

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  2. Hallo Bas, ik denk dat veel amateurs graag zo'n tuin willen hebben. Succes met het maken, ben ben benieuwd wat de resultaten zullen zijn. 73 Paul

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    1. Zeker in de randstad Paul. Maar het is natuurlijk altijd een keuze. Er zijn zat plekken in Nederland te koop met zelfs veel meer tuin als ik heb. Voor relatief weinig geld ook. Maar dan moet je niet opzien tegen een plek ver van de steden en jarenlang klussen om alles een beetje leefbaar te krijgen. Voor de hobby blijft er dan weinig tijd over. Dat merk ik met dat kleine stukje grond en een huis uit 1935 al. Maar ik mag niet klagen hoor, na 12 jaar begint het al wat te worden hier. 73, Bas

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    2. Wat de antenne betreft, ik denk dat het wel werkt. Maar de praktijk zal nog wel even wachten moeten. Het begin is er in iedergeval.

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  3. Hi Bas. I am VERY sure you won't be disappointed with a quad. Tips I would pass on: the fibreglass rods will not break, but they will bend a lot in high winds. This puts a lot of stress on the wire you use for the loops. I used 1.2mm drawn copper, but that would break after maybe 3 years, which is not very long. There is stainless wire from DX-Wire, or maybe try kevlar (but not the UL, thin stuff). Other wires, like flexweave, are too heavy. Also use stainless hardware. Attaching the wire with cable ties, even if UV-resistant, alseo leads to fairly rapid deterioration and breakage. Whatever you use, this is a fairly high-mechanical stress design in high wind areas.

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    1. Hello John, yes I realize this is a high mechanical stress design. Others did warn me for that. However, if you don't try you will never know...
      So far I wanted to attach the wires with hose clamps. But after one prototype I think 5 hose clamps are just to heavy. I think I will replace the clamps for cable ties and wrap them with vulcanizing rubber tape after installation. Since this is all a prototype antenna I don't expect it to last forever. I hope to learn what the weakest point is (the wires? Like you wrote). Ore something else? By making it as light as possible I hope the mechanical stress will be less compared to heavy materials. 73, Bas

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    2. Hi Bas. Yes, the rubber tape will be fine for some years, or you can paint the cable ties with white enamel - that worked well for me. Quads more than worth trying - they are the best antenna type where there is room available. Good luck!

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Thanks for your comment. Bedankt voor je reactie. 73, Bas