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1-5 of 5 messages
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Trap Vertical? or others? Looking to homebrew...
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by KC2ORG on November 15, 2006
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Hi all, I just moved into a new house with a few friends my brother in law works with. They are respect our hobby and find it interesting and fascinating, and have no problems with antennas out back.
My problem is this... I have a 40m dipole and a 20m dipole, cut very well so that they are about 1:1 across most of the band. I didnt want to go the route of having a windom or g5rv because i didnt want to have to mess with a tuner (i do qrp sometimes too, my antennas should be efficient as possible with out tuning them with a tuner)
I was looking into a vertical of some sort, something like the 6btv or so...but I was wondering how easy something like this would be to homebrew.
I have a large yard out back for the most part, and a few trees... outside of my window is a flat garage roof i can step out onto, back yard behind that. Would a vertical be a good choice instead of many dipoles out in the yard or a multi band dipole?
It's getting to be cold out... I'd like to get something up that doesnt require me to go out and move a tap or change antennas.
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RE: Trap Vertical? or others? Looking to homebrew.
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by G8UBJ on November 16, 2006
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If you have the space a fan dipole at a good height would be my choice.
http://www.hamuniverse.com/multidipole.html
They are simple to construct and for the money a 6BTV would cost, you could buy all the wire and insulators + support material you need.
My addition to the above design would be a good quality 1:1 balun
If you consider homebrewing a trap vertical take the cost of a 6BTV and double it, add a lot of hassle and away you go. That said a mono band vertical will gie good results and is simple enough.
73 Rex (G8UBJ)
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RE: Trap Vertical? or others? Looking to homebrew.
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by KC2ORG on November 16, 2006
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I didn't think a trapped vertical would be that hard to construct, if it were made from PVC and wiring from a local hardware store... i forgot about another kind of antenna... longwire/random wire/end fed... any input on these? I have a large distance between my window and some trees over by the fence... ~100 yards or so. would it beneficial for a wire to be put up there?
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RE: Trap Vertical? or others? Looking to homebrew.
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by G8UBJ on November 17, 2006
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I guess it wouldn't be so hard to construct a trap dipole but my feel vertical traps require a lot more work and effort for the results you will see.
Firstly you have to construct the traps for each band you intend to operate on and ensure the whole antenna has enough mechanical strength etc. You need to be able to adjust the element lengths between all your traps. Bear in mind that traps for a dipole are simple as they only have to deal with antenna tension. Vertical traps have to include torsional strength
The tricky part will be tuning it up. Before you start you really need lay down a good radial system (You will see lots of advise on this and it can vary from "Don't bother if you live on a beach/swap) to a highly elaborate buried system for the desert.
Ultimately you want the vertical to work against something. If/once you get the ground plane sorted start with tuning the highest band and work up.
Personally if you fancy going the vertical route I would buy a 6BTV and get that working first. Performance on 80m for that antenna is lacking but you could prove your ground plane works before attempting homebrew.
But it sounds like you have a fair bit of space. I would go for the fan dipole or maybe a trap dipole and if you have the time maybe an 80M mono band vertical. With 4 or more full size radials a full 1/4 would give you a good low angle signal (I think this would outperform an 80M dipole at 15M high)
If you haven't got any, buy some antenna books. The ARRL one is really good and includes the theory as well as lots of practical projects.
I think antennas are the last domain of the experimenter. Practice makes perfect and it takes experience and know-how to get the best results even from commercial products.
Have fun & 73 Rex (G8UBJ)
And remember what they say -
"If it didn't come down in the winter storms it wasn't up high enough"
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RE: Trap Vertical? or others? Looking to homebrew.
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by N3OX on November 17, 2006
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I'd stick with horizontals for the higher bands and go vertical for the lower bands since you've got space and antenna permission.
You probably *don't* want one antenna for all bands if you can avoid it. A vertical is best for those bands where you can't get a horizontal very high and want to work DX, but if your 20m dipole is at least ~25ft high, I'd not scrap it too hastily. You could trap it for 17 meters and up or go fan, though it would work well on each of those bands if tuned with GOOD matching networks.
A vertical would be the way to go for the low bands, though, especially if you like DX. If efficiency is your top concern, though, I can't really say you'd do better with a trap vertical than with a good set of matching networks on a plain vertical ... it's probably a tossup, honestly. I also think that an all-band trap vertical would be a frustrating homebrew project. I've built two-band trap homebrew antennas, but I wouldn't want to tackle many bands that way.
Here's what I did, just as an alternative thought:
http://www.n3ox.net/projects/lowbandvert
I didn't actually *build* 20m into mine, because I've got a 20m delta loop that I use also on 17m, once again matched at the antenna for good efficiency. However, a 40 foot antenna has a good pattern from 20m down, but 17m and above it has very high angle radiation lobes. This isn't the case if you trap the antenna, an advantage of a properly designed trap antenna.
Matching at the antenna with L-networks with good high-Q coils and good caps is going to be just as efficient as trapping, if not more. Both approaches would be pretty efficient, we're probably talking a dB either way. There is a disadvantage to my setup in that if I lose power, my vertical is no longer switchable from inside because I need +/- 5V to drive my motor.
73,
Dan
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