planning to build a 20m beam, but clearance UNDER and around the beam is at a premium

[mr_fx]

I am want build a 20m meter beam...

this is the requirements:

- cheap
- good clearances under and around the beam
- able to rotated by a cheapo radio shack beam...
- good gain

so far I have come up with a few posibilites

1.) Delta loop multi element beam...
2.) multi element V beam (elements sloping upwards, or sloping backward...)
3.) maybe a 20m copy of the Maco V quad?

I think I could use a larger PVC boom and a wooden rod on the inside screwed in for extra strength

and secure the elements to each other with some type of rope, or even thicker fishing line for that matter

 

[Captain Kilowatt]

20m is where things start to get big and using small hardware or thin tubing won't cut it especially if you have any wind or ice. Full sized yagi elements are over 33 feet long overall. Delta lop elements are about 22 feet on each side making it about 19 feet from base to apex. Either way there is a lot of inertia and I doubt a cheapo Radio Shack rotator would last long.

 

[w9cll]

Single band hex beam!

 

[Mudfoot]

Single band hex beam!

I've been looking at a Hex for a few years. I'm encountering more and more on the air.

 

[w9cll]

I will be putting up a 5 band one in sept.

 

[mr_fx]

I was kinda thinking about a delta loop quad beam, and using crappie poles for he main wire supports... would still be cheap and light

 

[mr_fx]

I should be able to make a light weight, 20m, 3 element version of the Maco V Quad (delta style cubical quad) http://www.macoantennas.net/files/Assembly_V-Quad.pdf

MAX-GAIN SYSTEMS, INC. : Fiberglass Price List

should be able to use this to fashion a 24 ft boom using 1" to as large as 1.5" 1/4 wall fiberglass tubing


as for the elements, I was thinking 1/4 fiberglass tubing, sleeved at the joints for length, this would also allow for length adjustments... of the wire elements...

tying the elements together with rope or even more fiber glass rods at the top corners SHOULD strengthen it even more

why I think this 'SHOULD' work for me:

1.) pretty cheap ($150 - $200)
2.) should perform well
3.) the element support rods will have almost 0 wind load
4.) cheap to repair of even rebuild if something should go wrong in the future

should be well under 20 lbs fully loaded

 

[Captain Kilowatt]

Single band hex beam!

That one slipped my mind. Might get by with a small rotator.

 

[Captain Kilowatt]

I should be able to make a light weight, 20m, 3 element version of the Maco V Quad (delta style cubical quad) http://www.macoantennas.net/files/Assembly_V-Quad.pdf

MAX-GAIN SYSTEMS, INC. : Fiberglass Price List

should be able to use this to fashion a 24 ft boom using 1" to as large as 1.5" 1/4 wall fiberglass tubing


as for the elements, I was thinking 1/4 fiberglass tubing, sleeved at the joints for length, this would also allow for length adjustments... of the wire elements...

tying the elements together with rope or even more fiber glass rods at the top corners SHOULD strengthen it even more

why I think this 'SHOULD' work for me:

1.) pretty cheap ($150 - $200)
2.) should perform well
3.) the element support rods will have almost 0 wind load
4.) cheap to repair of even rebuild if something should go wrong in the future

should be well under 20 lbs fully loaded

You will never get by with 1/4 inch tubing for the elements. If an owl should fart anywhere near it the antenna will collapse. You have to think about wind drag versus structural strength. long elements place a lot of stress on the mounting points.

 

[mr_fx]

You will never get by with 1/4 inch tubing for the elements. If an owl should fart anywhere near it the antenna will collapse. You have to think about wind drag versus structural strength. long elements place a lot of stress on the mounting points.

You think so? They will be mounted in a V pattern and tied together at the top

even if I went to a 1/2" fiber glass tube the increase in weight would be quite minimal

in fact I could use 3 telescoping sizes for the spreaders...

 

[wavrider]

Small foot print?

Light weight?

Cheap??

Good gain

Great F/B

DL7AOS 20 METER MOXON

everything you asked for.

 

[mr_fx]

that moxon is interesting

 

[wavrider]

that moxon is interesting

lots of info online google is your friend, even have moxon calculators.

it is a mono bander though.

Spider beam, hex beam are similar but different.

you need to get that beam 1/2 wl up in the air to get decent DX performance, lower well work but not that great.

 

[mr_fx]

lots of info online google is your friend, even have moxon calculators.

it is a mono bander though.

Spider beam, hex beam are similar but different.

you need to get that beam 1/2 wl up in the air to get decent DX performance, lower well work but not that great.

yeah I plan to mount about 35 feet

 

[Captain Kilowatt]

You think so? They will be mounted in a V pattern and tied together at the top

even if I went to a 1/2" fiber glass tube the increase in weight would be quite minimal

in fact I could use 3 telescoping sizes for the spreaders...

Supporting a downward force, like the weight of the element, is easy. A single half element spreader of a diamond shaped quad basically supports the entire antenna as the weight bears straight down. Now factor wind into the equation and start pushing the element sideways or towards the front or rear of the boom. Better yet watch what happens in wind gusts where one side of the element twists forward and the other side twists backwards. 1/4 inch tubing will never stand it. I may be inclined to use a few feet of 1/4 inch near the ends but the main portion or the spreader needs to be much heavier and using three telescoping lengths to add strength where you need it most (the boom attachment point) as well as maintaining lightweight materials is the better way to go. Just remember one thing however. Lightweight also means light duty. Building an antenna and putting it up is one thing. Getting it to stay up is a different matter altogether.