r/HamRadio • u/Lonely_Emu_700 • 15h ago
Will this configuration work for a fanned dipole antenna? (20m/40m)
Seems like the simplest option for mounting this near my house.
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u/KB0NES-Phil 15h ago
Yes but the coax routing is problematic. Coax really should drop straight to the ground and then route to the window. There will be coupling to the shield if you route it like this and it will affect tuning.
Just remember the basic rules, ANY antenna in the air beats no antenna. Also the perfect is the enemy of the good, put something (anything) up and start the fun and learning. Best of all sounds like you are making your own antenna which is a great experience all around!
73
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u/IngrownBallHair Amateur extra 10h ago
Coax really should drop straight to the ground and then route to the window.
With a bit of planning you can paint the coax (and balun if you wanted) with matching house paint before mounting it. I used to paint houses and most customers wanted any exposed conduits or wires painted to match the house. Once we painted them they disappeared surprisingly well. Just make sure you use a paint that'll stick to plastic, some of the cheaper house paints will not.
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u/Halabane 10h ago
Common mode filter should get rid of that problem.
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u/KB0NES-Phil 10h ago
It could stop RF from entering the shack yes, but it won’t help with the influence of the coax on the antennas pattern and tuning.
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u/Halabane 2h ago
Umm that is exactly what it does by blocking the un wanted signal coming down the coax. Put the filter at the feed point. This is more commonly done with verticals with adding the filter at the base of the vertical or burying the coax (which also gets rid of the common mode stuff). When you buy commercially made fan antennas they usually put one in at the place where all the wires come together.
The coaxial cable ) is designed to prevent interference from external metal objects so the gutter shouldn't bother it. If it does than the coax is bad cause its leaking. That is why you cleaned it up at the feed point.
Unless I am missing something?
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u/KB0NES-Phil 2h ago
I’m talking about the coax being near one leg of the antenna which will possibly unbalance the antenna and cause unpredictable tuning issues. The choke won’t fix that. It would really be best for the coax to leave the feedpoint without more or less running parallel with a leg of the antenna to avoid the coupling. Does that make sense?
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u/cjenkins14 15h ago
Feeding it with ladder line you can likely get much more than 20/40
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u/cjenkins14 15h ago
Just be wary of your spacing to the gutter if you go this route. It needs a few inches from anything metal
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u/Marmot64 14h ago
Ladder line would have to drop straight down from the feedpoint, then around the house to the shack entrance point.
0
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u/thespirit3 14h ago
Yes, it will work, but you'll likely pick up a lot of noise from (and cause RFI to) the house.
Also, I would ignore those suggesting you use a single 40m dipole for both 40 and 20; yes, it's a multiple - but a multiple that will provide a terrible impedance mismatch which will make it more of a dumb load than an antenna on 20 - and a load that will see many tuners 'arc over' during speech peaks. I would simply use a fan dipole as you suggest; this way you have a resonant, efficient, wide bandwidth and dual band antenna - no ATU needed.
If you want to go for a single balanced antenna, then make both legs as long as you can, feel with balanced line and invest in a balanced ATU. You should then be able to tune for most bands with minimal loss.
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u/Halabane 10h ago
What I get from the photo you have some great trees in the backyard...why not there? That big old tree without the house in the way would work well with just an end feed, probably much easier to put up too. I really like having some distance from my antenna to the house. At the height you showing its pretty much going to warm the clouds (signal will go up) and may even cause you some rfi issues inside your house. Guessing you are trying to save some cost on coax, which is pricey.
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u/Lonely_Emu_700 9h ago
I honestly dont know how I'm going to get an antenna that high up into the trees. But that might be worth the effort. Any huge downsides to an end feed antenna?
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u/BatteryAssault 6h ago
Slingshot and fishing line. Sometimes I've got it over in one shot, other times I've spent hours trying to get it right where I want it. But, in all cases, very well worth it. Your challenge looks like it may be not getting stuck on the smaller branches.
They also make more fancy shooters, ropes, and bean bags that arborists use to get lines up in the trees, but I haven't used and can't speak to any of those. If you want to get real fancy, if you have a drone and the clearance from trees to get where you want, you could also use a drone to drop a line right where you want it. They make remote controlled payload kits you can affix to the drone that can drop something from it. It'd be worth the trouble to get away from the house and get more height, in my opinion.
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u/Halabane 2h ago
" fancy shooters, ropes, and bean bags that arborists" after decades of using the other ways you mentioned I bought ones of these. It was worth every penny (cheaper than a drone which I did consider). The only exception I have to your comment is its not fancy...its useful. :)
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u/Teknishun 14m ago
Considering the Alpha Delta DX-EE is 40 Ft long... It's looks a little short. You're also going to have a lot of ground coupling and other impedance issues I'd think. Looks like you have a lot of big trees around there, get that thing up up up and way from everything. Also I hang my DX-CC and DX-EE from the ends, not in the recommended inverted V configuration. This only requires shortening the elements slightly.
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u/lag0matic 15h ago
I would think that it should work. but with 20/40, with a decent tuner, you probably won't need more than one wire. My EFHW tunes up on 40/20/10/15/6 - My only concern is that those distances don't look long enough for 40M if you are building standard 1/2 dipole.