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Best Plastics, Composites, Rubber for structural antenna parts

90329 Views 212 Replies 43 Participants Last post by  300ohm
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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I-Beams aren't so good, torsionally

You may end up with an antenna that twists in the breeze.
You may end up with an antenna that twists in the breeze.
Good point.

Maybe I can bend them in an L configuration... like angle iron.

Depending on what happens Sep 1/11, I'm hoping this will end up in my attic -- so no worries about wind. But I want to see how strong it could be in case it helps someone else pursue something similar sometime later.

I was just going to go ahead with 1x4 lumber, but thought this might have a bigger cool factor. :)

I have a real brutal SBGH made out of 14-gauge copper on a piece of plywood and no reflector -- so it's performance after the switch will have an effect on how fast I try this.
Tubular is good.

So is box.

Feel free to experiment, but tubes and boxes are used as structural elements for some really good reasons.

An L shape is a quarter of an I beam, so doubt it'd be stronger.
allanGEE said:
Maybe I can bend them in an L configuration... like angle iron.
Except that angle iron (mild steel) can generally withstand about 10,000 PSI of pressure while PVC or ABS... not so much. Not anywhere remotely so much! :D

I agree with those in the tubular/square tube camp for structural rigidity in plastic.

Okay, messed around a little this weekend with a length of 4-inch white PVC pipe I found in a construction zone dumpster.

Goal was to make some vertical pvc strips/planks to hold the reflectors and elements in place for an attic-mount SBGH-6.

I cut the pipe into a couple of 41-inch lengths (a little long to allow for trimming later) then ripped one cut lengthwise down the pipe on the table saw.

Then, using a heat gun, I spread the pipe open into flat sheets. I ended up with two sheets, about 41-inches by just a touch over 12-inches.

I ripped these in half to get the four verticals mentioned above.

Once you take the pvc out of its tubular configuration, it loses a lot of rigidity. I stiffened up the pieces a little by making a 90-degree bend along the length -- about 1/2-inch wide. Would have been better to have the same bend on both edges, but I didn't have enough pipe to give me the width I would have needed.

I've used up a good chunk of the pipe already, so will probably use some wood to finish off the build.

Overall, I learned enough that I think I would give it another go, with some design modifications and additions, if I ever need an outdoor antenna.

The stuff can be worked with any woodworking tools. The flattening process takes time -- but I have more time than money.

The process would be ideal for any smaller PVC pieces you'd want to make -- custom brackets for example.

I ran the video camera during some of the process, but haven't looked at how it turned out. If it's half watchable, I'll YouTube it and post a link.
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Red Snapper brand electric fence parts - at TSC store

RED SNAPPER brand, electric fence insulators and plastic support parts.

Look like they might somehow be useful as antenna plastic support parts, standoffs, or insulators.

Come in bags of quantity 10 or so.

I noticed them at the back of a TSC store in Brockville, Ontario.

TSC - "The Incredible Country Hardware Store"

160 Broome Rd, Brockville, Ontario.

Sort of Near a Hwy 401 exit.
N. Augusta Rd Exit off hwy 401 (exit #698).
TSC Store is sort of near / beside / behind the Brockville Wall Mart.

Brockville's - N. Augusta Rd exit off hwy 401 (exit #698).
Go in a northerly direction.
Then you hit Parkedale Ave E.
From there You can't miss the Wall Mart from there - it's right in front of you.

Sometimes that is a convenient place for me to stop and take a break while driving on the Hwy. So I stop and browse.

That TSC Store also has some excellent deals on some other things as well.

TSC stores are a chain - you may find them around in other cities as well.

PS. Also noticed 3/8 inch round, long, fibreglass rods, grey, pointed at one end, maybe 5 or 6 foot long for around $3 bucks each.
Same area of store.
"fibreglass rod post" (again used for electric fence applications I think)
Strong and flexible.
Might be useful for antenna builds.
Good insulators, strong and flexible. Reasonably priced. Probably last long outdoors.
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Plastic Plug for Half-Inch CPVC Pipe

I found these plastic caps for plugging the ends of the half-inch CPVC pipes I used on my GH10n3 antennas. They take up less space than conventional pipe caps. They are sold in the wide slide-out trays of assorted components at TruValue, for covering the heads of screws. Details in my photo album about construction of GH10n3 SNAP antenna.
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PVC, CPVC, Fittings UV protection

My understanding, is, for the fittings, they need to be dark pigmented, which are inherently UV resistant, thus the darker Schedule 80 PVC fittings would be recommended - but these run at least 3x more expensive than the white or the CPVC fittings...

However, when post-purchase protecting for UV, the suppliers recommend to coat them with LIGHT colored, 100% LATEX based, outdoor paint, for increased UV resistance...apparently LIGHT colored pigmentation provided the most Titanium Dioxide for UV protection.

Does this make sense ?
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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Black Tie Wraps

Thanks 300ohm, thats a good review!

Yes, I guess fuchsia wouldn't be an option :eek:

Are ALL BLACK tie wraps considered UV resistant...I've used some which were specified UV resistant, but many which are not specified, in either case after several years of wear they are still doing the job...
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 :eek:)

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.
Balun protection

I have noticed, that the balun connection feedpoint screws area on the DIY bow-ties are somewhat sensitive to the elements over time, specifically corrosion whereby the balun leads break off

Are there any recommendations for a simplePVC type enclosure built in at the feed point to cover the connection (it seems rather complicated to build into the structure and stand-off, and doesnt appear to create a perfect seal anyway since humidity/moisture will still work to the inside) ?

Typically I use dielectric grease for minimum protection, on a brass coated wingnut, washer, and screw.
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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I guess im trying to protect the connection itself, as opposed to the balun alone, like on the commercial antenna, CM4221HD

I tried to recreate the balun box protection, but it become too complex
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. :p

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.
I guess im trying to protect the connection itself, as opposed to the balun alone, like on the commercial antenna, CM4221HD
Condensation is going to last longer inside that plastic box, so it may actually speed up corrosion. On the other hand, it would protect the dielectric grease from drying out / washing away sooner from the sun and rain.
yes, im of 2 minds on that also, after all, the old CM4221 was exposed, then again they werent using brass screws and copper wire

I guess either way, it can be expected that eventually you may need to change out a balun
I came across this CPVC FAQs:

How long can CPVC systems be exposed to sunlight?

CPVC can easily withstand the ultraviolet exposure commonly experienced during the construction phase of a project, provided on-site inventories are turned regularly as would be anticipated. If CPVC is used in above-ground, outdoor applications, protection from ultraviolet attack can be achieved by shielding or by painting the system with an exterior-grade latex paint.
Looked at website referred to by 300 ohm.
It also has information about Solvent Cement Joining - applicable to ABS, CPVC and PVC, but not to Polyethylene (PE and PEX).

PE and PEX cannot be joined with solvent cement!
(My emphasis and exclamation)

The site's FAQs says the following about PVC's UV resistance and warns against using oil based paint:

Can PVC pipe be exposed to the sun?
PVC does not readily degrade when exposed to sunlight (ultraviolet radiation) due to natural UV inhibitors present in the material. Short-term exposure to sunlight, such as during construction, is typically not a problem for PVC pipe. PVC piping may be used in outodoor applications when the piping system is painted with a light-colored water based acrylic or latex paint that is chemically compatible with PVC. When painted, the effects of UV exposure are significantly reduced.

Does long term exposure to sunlight degrade exposed PVC pipes?
PVC pipe contains stabilizers to protect the pipe against attack by UV present in sunlight. After several months of outdoor exposure a discoloration may appear on the surface of the pipe, however, the performance of the pipe is not affected. After two years of exposure, there is only a slight reduction in the impact resistance of the material. PVC pipe used in permanent outdoor exposures should be protected by a light colored compatible water based paint. Do not use oil based paints.
I used solvent based paint on some white PVC fittings in my GH build, but by pure luck I primed them with Zinsser 1-2-3 latex primer first. The can says it's "Excellent" for PVC, so I should be OK, eh? :D
I used solvent based paint on some white PVC fittings in my GH build,
Yeah, I used the cheapest flat 96 cent indoor/outdoor spray I could find on my first GH build that used white pvc (that was before I discovered the grey stuff, heh). After 3 years, its held up very well outdoors. I only used 1 thin coat, just enough to cover. Using many or thick coats it will peal, whereas 1 thin coat will just slowly fade. Ive also done the same on outdoor white pvc trellises and sump pump drains for over a decade, and theyre still in great shape. Kelly green blends in nicely with leaves and grass. :)
Zinsser 1-2-3 latex primer is good stuff and I use it on wood. But for pvc its probably overkill.

PE and PEX cannot be joined with solvent cement!
Plumbers Goop works fine with PEX, at least for antenna usage. Maybe not for water pressure though. Im not really a big fan of using PEX for water usage either. The connections just seem weak and flimsy.
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