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Best Plastics, Composites, Rubber for structural antenna parts

90318 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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ha ha ya, when your on the lookout for parts you look at everything in the store in a different way. I was thinking some old tent poles would work nice but the ones I had were too skinny.

I'll post a pic of what I come up with this weekend.
Hey, skinny, if strong is good :p
mrplow, you have quite a task to solve. In addition to supporting and retaining the rods, the material you find must be bonded or mechanically fastened to the pvc spine. Pipe cement makes more of a solvent bond than act as a conventional glue. No amount of it will make a good joint with an incompatible plastic, and it may ruin it. On the other hand, most glues, such as epoxy, will not bond to pvc. Have you considered making a collar for each pair of rods that would slide over the spine, a donut that has an arm sticking out from each side to support the rods? They would need to be fabricated, drilled with precision to get the rods to be in proper alignment. They could be made from architectural pvc sheet, which would bond well onto the spine. This sheet is expensive, sold in 4' by 8' sheets, but I get scraps of 1/2" (true) thickness from renovation jobs, it is used to replace white wood trim. I cannot say that 1/2" thick would be strong enough, but it may be available in 3/4" thickness. The spine would be drilled thru to just pass 1/4" rod, as would the collar and its arms. A steel rod would be passed through to align the collar with the spine holes when the collar is cemented in place. At least two size collars would be built, one for those rods that have a small inner gap, another having longer arms for the rods having a bigger gap. I have thought of a couple ways to secure the rod in its arm. In one, a small round notch would be made in the side of the rod, and a hole would be drilled partway through the top of the collar, offset from the centerline of the rod. With the rod inserted so the notch aligns with the hole, an aluminum pop rivet is inserted into the hole and popped. The inner rivet material should flow into the notch and fix the rod in place. Another would be to slit the end of each plastic arm near its outer end. The rod would have burrs raised on it by a center punch or by clamping it in a flaring tool. Once the rod is inserted, cement would by applied into the slit in the plastic and the slit clamped shut, which would secure the rod with the correct inner gap and keep it from working its way outward.
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GH10n3 Using 3/4" PVC Spine

mrplow, more comments re GH10n3 having 3/4" pvc single spine. My first thought when designing my GH10n3 single spine was to use 3/4" pipe, but I could not find elegant solutions to the problems you are currently working. I also was going to use 3/8" tubes, which pretty much dictated using 1" pipe spine. I have been thinking about how you would attach and support the reflector rods, but I would like to know how you propose to support the active elements and NARODs, which would seem to me to pose similar problems using the 3/4" spine.
Since my posting above, I have thought of a simpler way to fix a solid aluminum rod or a tube inside a plasic assembly such as my outside collar scheme having two arms described in posting just above. This would also work if the rod runs through a plastic tube, if you find a suitable one. The rod would have a notch filed in one side, and the plastic part would have a hole drilled crosswise to meet the hole through which the rod runs. When the notch appears at the bottom of the crosswise hole, the rod is in position to create the proper air gap. Chips of pvc would be stuffed down into just the bottom of the hole and into the notch in the rod. That plastic would be melted using the narrow tip of a temperature-controlled soldering iron or the flame of a micro-torch at its lowest setting. The soft plastic would be tamped using a metal rod. More pvc chips would be dropped into the hole, melted and tamped to create a plug that would key the rod in place.
Have you considered rolling your own tubes from cpvc? You could make a holder for slitting 1/2" cpvc pipe sections, shown in my SBGH6 Instructables series, cut out enough material that the remainder could be warmed then rolled to fit a 1/4" rod. CPVC can be heated to a point that it will yield without melting. Once cooled, it will retain the new shape. There has been a recent posting, probably in this thread, that has the temperatures at which cpvc can be worked without damaging it. If the slitting is done just right, it might be possible to cement the seam together to give the tube maximum strength. You might need to build a hinged mold that would close to roll the tube into its final shape. The plastic could be slowly heated in place using an electric heat gun, until the mold can just be closed. You would drill a hole through the spine sized to be a tight fit with the outside of your homemade tube, with the metal rods already fixed within the tube. Tapering one end of the tube before it is warmed would make it easier to insert the homemade tube through its spine holes. The tube would be marked to indicate when it will become centered in the spine, and pipe cement would be run around the tube just before it is slid in the final quarter inch.
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mrplow, you have quite a task to solve.
Tell me about it, I have hot glue burns on my hand.

but I could not find elegant solutions to the problems you are currently working
Everything is just pressure fitted so ya its definatly not elegant. I did use teflon tape at least.

In addition to supporting and retaining the rods, the material you find must be bonded or mechanically fastened to the pvc spine.
how you propose to support the active elements and NARODs
Well I found some flag poles at the dollar store that I have attached to a 1/2" plug inside a 1/2" T joint for the elements. The same poles are used for the reflectors.

The 3/4" spline is connected to a 1 1/4" 4 way spliter to connect to the mast then on the other side of the splitter will be a 1/2" reducer with 1/2"pvc with a hole for the NAROD.

So far all the reflectors are in and all thats really left is to bend and attach the element and NARODS. Everything is solid except for the T-joints connected with the flag poles to hold the active elements. They rotate but that should be fine ones the elements are attached and holding it in place (I think). I'm too tired tonight to finish it but there were defiantly some of my self imposed design flaws I had to work with. I'll post finished picks tomorrow.
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well the antenna was finished off crudely because I couldn't find a home depot bad with my good uv protected zip ties, nuts and bolts to secure the balun to the element and I'm also missing those 'p' shaped cable clamp things. So I ended up using cheapy computer cable ties for everything, all strung together for long sections. Also my horrible non strait drilling didn't help to keep the reflectors and NARODs parallel. Oh ya I had to use electrical tape to hold the balun to the element. I wonder whats hurting the performance the most, so much to choose from.

Once I find more supplies I'll take it down and try to align everything. Perhaps a couple tents poles horizontally could keep the reflectors aligned.

Replacing my crappy free antenna that had multiple broken fittings gave me NBC but I also lost ABC.

my free antenna, it came with the pole and broken rotor, well its probably broken, its super old and doesn't had a control box. Yes it snowed April 18th.

there she be

wow I suck. Notice how the inside of the element is bent towards the reflectors. Hey at least all my rods are the correct length.
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Get Jiggy With GH10n3 SNAP

This is the framework for my second single-spine GH10n3 antenna for this model: More photos, with captions, appear in my album GH10n3 SNAP (see also my photo album about first GH10n3). My first GH10n3 works great, but my construction was not first rate. Neighbors have expressed interest in building one, and this SNAP version does not require precise drilling of the spine, merely careful drilling of a simple jig that exactly locates all the parts of the antenna with correct spacing and rotational orientation. I took the design to the limit of low weight and low cost, using 1/2" CPVC pipe and fittings. This pipe is strong but limber, so the antenna must be connected to a rigid mast, which can be metal, mine is 1-1/4" dia. The same jig concept could also be used to make the antenna using 3/4" CPVC pipe and fittings or 1/2" PVC sch 40 pipe and fittings. In fact, the jig I made can be used as-is with these materials. Bushings made by drilling short pieces of 1/2" PVC pipe can adapt the 1/2" CPVC pegs I use with the jig so they will work with 1/2" PVC fittings. I would still use 1/2" CPVC tees facing crosswise across the spine to accept the active element and NAROD supports and the reflectors. Short 1/2" CPVC pegs, and bushings made from drilled-out 1/2" PVC pipe, allow modified 1/2" CPVC tees to attach to modified 1/2" PVC tees.
My supports for the active elements and NARODs for this antenna will be similar to the ones in the album for my first GH10n3, except that parts will snap in place. My reflectors will be pre-assembled modules that will also snap in, similar to what appears in my Antenna Craft photo album. Those use 3/8" dia Al tubes from defunct commercial antennas, but 1/4" dia Al tubes could be used as well as a single fiberglass rod having metal applied to its outer lengths. Each option would have its own method for securing the rods within the modules. I do not think I would use solid 1/4" Al rod for the reflectors on a 1/2" CPVC spine.
I intend to detail the entire construction of this antenna in a project at and will post a link to it in the thread "Top Hat" GH with NARODs for VHF-HI: Major GH Improvement. My existing GH antenna projects at can be viewed by entering unclesam in the home page search box. On the new page, click "NEXT" repeatedly to page through them all. Creating a free, risk-free login will subject you to fewer ads and allow you to use more features.
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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 :p)

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.
I'm Ready for My NARODs, Mr. DeMille

Completed framework for GH10n3 SNAP. Next come active elements and NARODs made from 1/4" copper tubing. Support for stub ends of elements and NARODs is simplified from those on my first GH10n3. Still wrestling with what I will use for reflectors. Another method for covering fiberglass rod with metal is to use tinned woven copper wire shielding, which is sold in different diameters by the roll. Just slip a length over each end of fiberglass rod, like of some kind that is open at one end and closed at the other. Kind of costly material, though.
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How to Buy Unbent 1/2" CPVC pipe

The holes in the predrilled metal parts of the single-spine GH10n3 SNAP I am building mated perfectly with those in the predrilled plastic frame (see my photo album). This was made possible by assembling the frame using the jig, no trimming or bending was needed. Success of this design depends on finding straight sticks of 1/2" CPVC pipe, which will not be found in hardware store or home center out-front displays. Ask to choose your own from back in the stock room, which will more likely be approved at a small local store. Pipes will be taped into tight bundles of about ten ten-foot sticks, just as they came off the delivery truck. Being bundled helps them remain straight. If the bundle looks straight, the pipes at its center will be straight. You can push out a couple of the center sticks without undoing the bundle.
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What fittings for connecting 1/2 inch fiberglass rods?

I am contemplating to build an antenna frame using 1/2 inch fiberglass rods. But have not been able to find proper (plastic/PVC) fittings to connect the rods together. Any suggestions?

One thing I thought of is to use 1/2 inch PVC fittings with a piece of schedule 80 pipe glued in first. The 1/2 inch schedule 80 pipe has an ID of 0.548. It's a bit larger and could be loose. Also, I know the PVC pipe ID may vary a lot.

An alternative is to use 5/8 fiberglass rods and 1/2 inch copper fittings. The negatives are the metals and more weight, which I want to avoid.

nav0239, the 5/8" dia fiberglass rod ought to be a perfect fit in CPVC plastic pipe fittings, like those shown in photos above of my GH10n3 SNAP under construction. 1/2" CPVC pipe is 5/8" outside diameter. Before mixing plastic pipe with fiberglass rod you may want to do some bonding tests. The cements sold for glueing plastic pipe and fittings are not traditional glues, but create a "solvent" bond. They dissolve the two surfaces, which quickly harden again into a single material. They may temporarily stick fiberglass rod in place, but may not produce a permanent strong bond. On the other hand, ordinary glues will not stick to PVC or CPVC.
Hi unclesam, thought the OD of 1/2" PVC pipes is 0.840". While 5/8 is 0.625.

You are right on the glue part. I will have to do some experiments as you suggested. Maybe some cauking or roofing tar will work if there is a good enough fit?
nav0239, I should have put more emphasis to remove confusion. It is 1/2" CPVC pipe (light tan color) that is 5/8" dia. CPVC is still sold in home centers and hardware stores, though the displays are steadily shrinking. Most of the store clerks have never even heard of it. Some epoxies will adhere to plastic pipe fittings, but you need to really rough-up the surface to get a bond, which is also true for bonding to fiberglass rod. Do report your results for which adhesives and methods of preparation work.
I found some PVC Conduit Support Straps at Lowes the other day.
Take a look at my Design_Pics album too see how I used them.
They make good mount platforms and are UV inhibited for use in direct sunlight.
You can buy them at most home improvement\hardware stores

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PVC Strips and glue to mount elements

If you build a frame of schedule 40, and lay the GH elements on top, could you use small pieces of schedule 40 (perhaps notched) and put them on top of the elements with glue at each end where they come in contact with the frame?

Below is not to scale obviously, but may be better than the above explanation.

____/--------\______ Clip/fastener either side of and on top of element
_________________________ Frame

O = Element, ignore the "..." I needed them for spacing.
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Flat ABS material from round pipe

'Nuther thought that I may try out unless someone has info that would indicate it's not worth it.

If I run a length of abs pipe across my table saw, cutting it along it's length, then I may be able to heat it up with a heat gun and flatten it out.

1-1/2" ABS would give you a strip over 4 inches wide (ideal for a GH with reflector), and the thickness should provide a lot of stability. A 2" would give you a 6" wide strip.

Pieces could be assembled with ABS Glue for a non-conductive weather-proof frame.

I imagine you could even build an ABS "I-Beam" spine by gluing three strips together.

For a GH with Narods, you could cut 3 or 4 matching strips that would run top to bottom, and you could drill holes in the right location to mount the elements.

Can anyone spot any fatal flaws with this idea?
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Oh Thank Heaven!

I recently stumbled upon a ready source of 12-inch long 1/4-inch dia plastic drinking straws for experiments, the kind that do not have the corrugated flex feature. See my photo album for additional photos. 7-11 Stores offer them with their Big Gulp drinks, for free. I have done no more experiments with the concept of making active antenna elements by wrapping Al tape around the straws, but I may now that I found this source. The recent hurricane knocked out grid electrical power in my rural mid-Atlantic U.S. area, which usually means 5 or more days in the dark. By some fluke in the space-time continuum, a 7-11, which I ordinarily would never have visited, is the only business anywhere around that has grid power (no generator), has been selling a lot of food, ice and gasoline. I was glad to find I would not need to eat dust bunnies and lick dew from the driveway (again), and the straws were a happy bonus. We here at Do Little Farm hope that some day there may be a way to predict storms like this one and maybe some sort of public announcement could be made in advance. I am still on netbook battery power, but thought this find of the straws was important enough that I modified an old razor blade radio so I could get out the word via broadband.
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If I run a length of abs pipe across my table saw, cutting it along it's length, then I may be able to heat it up with a heat gun and flatten it out.


Pieces could be assembled with ABS Glue for a non-conductive weather-proof frame.

I imagine you could even build an ABS "I-Beam" spine by gluing three strips together.
It may be an interesting experiment, but I think you are going to have a tough time flattening out the plastic. I think it will be difficult to get it to a uniform temperature where it will be pliable enough to flatten without melting the surface. Even if you do get it flat, when it heats up with the sun shining on it the stresses you have put into the plastic may cause it to warp. Let us know if you have any success.

There are stores that sell stock shapes of various types of plastics, so it would probably be a lot less work and not much more money to buy some flat stock to create your I-beam structure.
Salvaging PVC From Pipe

Well, a little bit of serendipity...

Out for a walk last night, through a neighborhood with lots of new construction.

Someone had tossed a 10-foot length of 4-inch PVC conduit in a garbage bin. It was actually sitting inside a length of ABS, but the ABS was wedged in tight under lots of debris.

Came back with the van and grabbed the PVC conduit though. As soon as I have time, I'll try and make flat pieces out of it as per above. May take me a while to get around to it, but will post results when I do.
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