Best Plastics, Composites, Rubber for structural antenna parts

90276 Views 212 Replies 43 Participants Last post by 300ohm, Oct 10, 2013

stampeder

Discussion Starter · Nov 26, 2008 (Edited)

Just a warning note about using ABS for structural parts that I've mentioned many times before - hopefully what you're planning to use is the thick walled stuff that has little or no flex. If you go to Rona or Lowe's or Home Depot and shake a 10 foot ABS pipe like a sword it flexes a lot.

It seems to be rigid, but its not. If you shake a length of PVC like that it will seem like a wet noodle, so avoid using PVC for structural use either, except when recommended in build plans.

From experience I'm clarifying that ABS should never be used as a pole or mast, and it should be carefully considered if you're thinking of using it as a horizontal boom of any length more than a meter or a few feet.

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300ohm

· #120 · Aug 5, 2010

Good link. Three way ells and four way tees and 5 way crosses are a rare commodity.

With the beveled ends on their fittings, they definately had pvc furniture making in mind.

300ohm

· #122 · Sep 23, 2010

For a short section a replacement fiberglass rake handle may be readily available. Unfortunately I'll need a 12ft length to upgrade my yagi.

Yeah, and Ive seen some of those rakes with fiberglass handles available for as low as $8. You could always join them together with a short insert piece, and fiberglass the sections together with fiberglass cloth and epoxy/polyester resin (available at Pep Boys etc or marine stores). Fiberglass boat outrigger poles also come to mind for long sections, but new they are pricey.

I'm considering a single vertical pole design for my new one as I've seen some nicely built ones on this site and the heavier elements/reflectors may not require the support of the rectangle. Windage and less components are in the plus column for the single pole design but I wonder if I should stick with the rectangle due to the occasional but mostly heavy snow we get here. What do you think?

My co-linear rod reflector DBGH build used a single middle pole. I used 1" pvc (the grey electrical stuff is cheaper and UV resistant) with broom handles, covered in polyurethane construction glue which expands as it hardens, shoved up the middle for stiffness. Its held up very well.
A fiberglass rake rod up the middle, if it fits, would do the job with even less weight.

300ohm

· #125 · Sep 23, 2010

Ahh yes, I ran into the same problem when trying to order greenhouse polycarbonate panels, like Norm Abrams used on NYW. The crating and the freight just became too non cost effective. I had to settle for the inferior single layer Lowes polycarbonate panels. They work of course, but they have more heat loss.

300ohm

· #128 · Oct 18, 2010

The good : The points where the plastic touches the metal, because they are at low current points, should have the least effect on the antenna.

The bad : Those are going to be tricky cuts. (although on a table saw, with the right diameter blade, it may work out)

300ohm

· #131 · Nov 26, 2010

Unfortunately, thats pretty rare stuff and in most cases would have to be ordered online and the cost would be pretty high.

If an item can be found that uses square fiberglass tubing, at say a flea market, then it would be great even if it has to be pieced together. Piecing fiberglass together isnt too much of a chore.

300ohm

· #137 · Jan 5, 2011

I compiled tricks for working with plastic pipe and fittings which could apply to building any version of the antenna, posted them with lots of photos at Instructables.com

Step 1 Sled - You really dont need the sled for the sharpie, as the point is to get an initial straight line on the pipe. I just lay the pipe on a flat surface, use pony clamps to hold it in place, lay a pencil or sharpie also on the flat surface and run the pencil/sharpie down the pipe.

Step 2 - Mark Pipe Quadrants Without a Circle Template, is a very good tip.

Fold the paper in half for 180 degrees and fold again for 90 degree marks.

300ohm

· #139 · Jan 12, 2011

Thats very similar to the way I built my first rod reflector GH.

But using UV resistant grey pvc gutter ferrules is much simpler, cheaper and the pvc gutter ferrules fit the 3/8" aluminum tubing perfectly. Because they have small ridges on the inside, they touch the metal less, which means they change the velocity factor of the reflector rod less. The aluminum rod can be affixed to the ferrule either by a dab of plumbers goop on the inside or pop rivets or screws.

They are available at ACE Hardware stores (at least mine) for 15 cents apiece. Home Depot also has them, but you have to buy the multi packs with the gutter nails for more money.

300ohm

· #140 · Jan 12, 2011

This could be a useful item for fabricating plastic high density polyethylene (HDPE) antenna parts :

Thing-O-Matic by Makerbot

http://www.dailymail.co.uk/sciencet...ble-factory-box-create-3D-object-plastic.html

300ohm

· #143 · Jan 13, 2011

For my GH103nXmas, I intend to pop rivet the rods inside short 1/2-inch CPVC sticks, rather than use the PEX inside CPVC.

That would be OK as long as the 3/8" tubes are along the same side of the CPVC tube, and you mount them all consistently and compensate for the extra distance. One downside could be that the gap turns into a whistle, heh. That could be fixed with some silicone or other sealant, but then a weep hole may have to be drilled to let out condensation moisture.

My first attempt was with the gutter ferrules, but I tore up the interior ridges trying to push the rods in, could not get them go go in, my rods might have been larg-ish.

And it could be that the ferrules on your particular production run had excess plastic waste on the ridges (I forget the term thats used, heh). Predrilling with a 3/8" bit should have taken care of that.

300ohm

· #146 · Jan 18, 2011

The best source for HDPE that I have found is old blue or black plastic barrels that industrial fluids or foods are shipped in.

From my observations, mushrooms are shipped in blue barrels, pickles are shipped in black barrels and peppers are shipped in red brick colored barrels.

300ohm

· #149 · Jan 19, 2011

I ran across a web page where someone tried to put a funnel on the front of a hot air gun and make his own hot air welder. He wound up melting the hot air gun because it didn't have enough air flow to keep its case cool. With some modification, that idea might work.

Some heat guns are made of metal and some have slot type funnel attachments. Theyre pricier of course.

One idea is to cover the areas NOT being bent with oversize aluminum pieces to dissipate the heat away.

300ohm

· #151 · Jan 24, 2011

The antenna is optimized on channel 21 (using the program 4nec2) with a net maximum gain of 18.1 dbi. I built the antenna from ¼-inch diameter aluminum rods for the zigzags, a 3/4 x 3/4 mesh split screen

For channel 21, the difference in gain between 2 X 4 mesh and 3/4 X 3/4 mesh is pretty small. 3/4 X 3/4 mesh is going to catch a lot more wind and debris.

For a reflector that large, I would build the frame from 1/2 inch EMT pipe. Essentially I would have a left side frame and a right side frame and connect the two sides with pvc pipe, so there is no electrical connection between the two sides for the split reflector.

3/4" pvc ells and tees fit 1/2" EMT pipe fairly well, but not perfectly. Screws or rivets would hold them in place.

300ohm

· #156 · Feb 7, 2011

Looks really nice. Overkill for an attic, but nice.

300ohm

· #160 · Apr 15, 2011

UncleSams frame, while overkill even for me, is a decent design.

See, part of the fun for building your own antenna, is figuring out using your own locally available low cost supplies to build a superior antenna, if you know what I mean.

A cheaper superior build is always better.

300ohm

· #162 · Apr 15, 2011

Hey, skinny, if strong is good

300ohm

· #168 · Jun 21, 2011

Looks like Gorilla Glue - Quick Cure, will work for bonding styrofoam and metal together. (and styrofoam to styrofoam along with bonding a host of other materials)

Do not use superglue/krazy glue/cyanoacrylate. It reacts with styrofoam to create a nasty little cloud of cyanide vapor, from what Ive read. (I dont think Ill test the validity of that claim, heh

)

Styrofoam sheet backing is a nice way to make an attic GH. I would apply the Gorilla Glue - Quick Cure glue at the midway points of the stubs and legs.

300ohm

· #189 · Nov 16, 2011

Yeah, schedule 80 stuff is pricey. But the grey electical sch 40 pvc is half the price of white pvc sch 40 which is about 3/4 of the price of cpvc. I dont know how long cpvc will last outdoors, but probably longer than plain white pvc.
Thats the situation on the pipes.

For the fittings, common tees and small elbows for grey electrical sch 40 arent carried locally (couplings are though) and have to be special ordered at a higher price. Sch 80 are also expensive. White sch 40 fittings are the cheapest and because they are thicker than the white sch 40 pipe, they will naturally last longer outdoors than the white pipe.

Some latex paint sticks very well to pvc, while other latex paint will peel from pvc fairly quickly, Ive observed. There is Vinyl Color spray paint sold at auto stores which is really a dye instead of a paint and sticks to pvc very well. The ordinary cheapest spray paint will also stick well if used in thin coats, as evidenced by graffiti everywhere heh. Thin coats of any paint will last longer than thick coats, as thick coats have a tendency to peal. Pretty much any paint is better than none for long term protection.

Yeah, Ive read the light color vs dark color debate on various paint websites. For most people, theyll want to use a color to make the antenna inconspicuous to the eye. Flat colors will do that best.

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300ohm

· #191 · Nov 16, 2011

Fuchsia fine if you have a fuchsia colored house. My brother has a woman in his neighborhood who has bright fuchsia colored siding with a black roof, heh. (She likes the color fuchsia

)

but many which are not specified, in either case after several years of wear they are still doing the job...

Thats good to know. I usually try to buy ones that say UV resistant on the package (they could be lying anyway), but some at Harbor Freight dont and I wonder about it.

300ohm

· #193 · Nov 28, 2011

This is what I did to protect the balun on my curved mesh GH10.

Theres also weep holes drilled in the bottom to let any water that does get in, get out fast.

Nothing glued, just #4 wood screws to hold things in place.

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300ohm

· #195 · Nov 29, 2011

Grey pvc electrical boxes could also be used as balun protection.

Ill repost this here in the plastics thread.

White nylon cable ties do have a use outdoors : as automatic timed release devices.

On my first DBGH colinear rod build, I used fiberglass tent poles and cable ties to keep the rods in place and in plane. I had glued the rods into the pvc pipe with Plumber Goop. Since I used white nylon cable ties, they deteriorated after about a year and half and the fiberglass tent poles fell off by themselves. The Plumber Goop in the meantime had fully hardened, and when the fiberglass tent poles fell off, the reflector rods remained in perfect alignment.

Even though I did that by accident, it could be a good tip for someone with a tall tower thats not easy to climb.

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