Advice on constructing HF antenna | European Hamradio portal

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Visitor
Anonymous he September 9, 2015 at 12:03#11427
Hello everyone.
After recently renewing my license, I would like to build an HF antenna. I would like to reach out to everyone with experience for constructive advice. The ideal antenna - an invisible multiband. I am thinking of a quad loop 80m resonating on harmonics driven by a 1:4 balun. I would mechanically 'fold' the antenna a bit - 'squeeze' it with a shoehorn onto the parapet of the neighbor's apartment on the top floor. So far, he has no problem with it. The coaxial lead would go directly into my room - ham shack on the 3rd floor.
I attach a preview of the parapet of the highest floor of my house where I currently have access.
In the corners of the parapet, I would place 1m fiberglass rods, between them I would stretch nylon and attach the antenna wire to it. The wire is 1.8mm enamelled.
The problem is not so much the mechanical construction, but that there is sheet metal all around the parapet + metal railing = short circuit. The railing I could theoretically 'cut' somewhere, that might be possible.
It's about how to build an invisible multiband antenna, as little affected by nearby metal objects as possible. Advise me what I should place there according to you, considering that I may not have access there anymore.
I will be grateful for any advice.
Ľubo - OM6ADP
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Visitor
Anonymous he December 27, 2015 at 19:49#14236
Such a loop can work, but it has several buts.
It will not be delta, nor quad.
You will have to give up some band when the loop of the parapet will create a short circuit in this band, or maybe this only band will radiate well.
It is certain that the antenna conductor should be as thick as possible; an older type of coaxial cable, RG2013, which due to its large diameter of the braid, will replace the unsightly AlFe rope, is sufficient.
For the loop to work at least somewhat optimally and not show excessive losses in power supply, it is ideal to install the SGC remote antenna element for powering the loop.
It works not only as an L element but for low impedances, as a full-fledged PI element.
I have tried it, but not very verified.
The entire antenna construction may not ultimately work satisfactorily; it's simply a lottery.
Without more precise measurements and experimentation, it is not possible to draw any specific conclusions.
The experiment is cheap, but we somehow earn little...
http://www.sgcworld.com/239PROductPage.html
http://www.sgCWorld.com/Publications/Manuals/239man.pdf
In that PDF manual on the last page, there are options for installing not only dipole but also loop antennas on various vehicles and objects.
The loops worked well.
To control the SGC 239, you need nothing; just provide it with a power supply of 12V and it works autonomously.
The loop you designed will probably work too.
Due to lower bands, especially 80m, it is good for the antenna conductor to have the lowest possible specific resistance; otherwise, losses increase disproportionately and the joy of the connection decreases.
Otherwise, it is likely that you wouldn't even have to deal with the loop; it is possible that if you can find suitable connection points on the attic using delta or gamma power supply, or double gamma, you can achieve results without the need to stretch the loop. An antenna scope or MFJ analyzer, etc., will help a lot.
The problem will be that all interference that spreads in the house, if it is close to the resonance of that antenna, will transfer to the TRX and vice versa; RF propagation will crawl around the house.
But you cannot avoid this, even when constructing the loop on insulators.
I verified this a year ago on a shipping container, where I used magnetic holders on skis to attach PVC pipes from the side and stretched the loop above the container.
However, I did not have good results because I could not dedicate enough time to it.
Happy and cheerful!
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Participant
OK1FTJ he December 28, 2015 at 19:23#14237
This solution near such massive conductive structures will not be ideal. Paddle antennas are almost better. The expected power to the antenna, which then causes TVi interference, is also a question. Sometimes a regular vertical or one of the LW antenna variants with a quality antenna element is a more acceptable solution. In residential development, it is always about some compromises.
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Visitor
Anonymous he December 28, 2015 at 21:32#14238
Ľubo, build that antenna, you will be satisfied with it. SP7LTA specifies the length of the loop.
82.84 m, powered through a 4:1 balun.
I also have a loop, I use it on all HF bands. On 2 m and 70 cm
it also works. You will be surprised by the quiet, clear reception. Best 73! Vilo, OM3CAQ
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Participant
om1aeg he December 29, 2015 at 13:00#14239
Vilo, the perimeter of the space where you want to put it is 56m... Check the sketch...
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Visitor
Anonymous he December 29, 2015 at 19:53#14240
Tóno, the sketch does not display for me, it reports 'Server not found'. But other loop sizes also work: http://otc.CQ.sk/index.php?option=com_content&task=view&id=449
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Visitor
Anonymous he January 1, 2016 at 10:28#14241
All the best in 2016... 🙂 greetings to everyone, thank you for the advice.
I tried the antenna up on the roof and it was 'quiet'. 84m stacked on a perimeter of 56m... I was really sad about the result, but it was just a test to see if it would work. My previous end-fed 42m dipole performed incomparably better. I compared them against each other... Currently, I have an isolated passage through the wall to the tuner by the window and a dipole 2x41m outside. An invisible 0.3mm lacquered wire thrown into the trees. For reception, this is more than enough for all bands. In the spring, possibly when I finally buy a tcvr, I will try to replace the dipole delta/quad with a loop anchored to the opposite trees. The height of the antenna isand will be about 15-18m above the ground. Hopefully, it will work.
Currently, I am only listening with a cheap SDR.
Anyway, I will let you know when I make progress.
73 from OM6ADP
Ľubo
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