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PE4BAS Amateur Radio Weblog

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

Posted: 24 Oct 2021 01:03 PM PDT https://pe4bas.blogspot.com/2021/10/5-band-quad-hf-antenna-design-building.html


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 2,85 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.

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