: Best Metals for Antennas: Performance, Soldering, Welding, Bending, Working
2011-06-26, 09:19 PM
you might want to consider the single-spine GH10n3 SNAP that I am working on.I may very well try your SNAP design. I haven't studied it yet but it sounds great! I've decided I will try a double vertical GH next time so I'll be looking at your albums with great interest.
With your SNAP design could you try many different materials as long as the form factor was the same - 1/2" dia. ? For instance 1/2" tubing wrapped with Aluminum tape or aluminum foil secured with Tuck tape? If it didn't weather well it would be simple to replace if the antenna was reasonably accessible.wind a narrow strip of it around the rod in a spiral, secure it at both ends.Or aluminum foil held on by contact cement in a spiral wrap.
BTW the tubes actually come out at about 5/16" since they are formed around a 1/4" rod. It wouldn't be necessary for the active elements, only for the narods and reflectors. I've decided I have to improve my methodology to make them as well so I will add your idea to my manufacturing steps. I will keep you posted as to results when they happen. By the way, I'm notoriously slow!
As well your idea would save a bit of money too since those damn fiberglass driveway reflector rods aren't inexpensive whereas the aluminum flashing cost me less than $12 for the whole antenna and I had some left over.
2011-06-28, 12:03 PM
I looked at your SNAP design and see that it would have great potential as a kit. For someone on the thrifty side (read cheap) like me though it requires too many fittings and actually quite a lot of preparation. I think I will stick with my original method which basically needed no Ts or fittings except for the endcaps I used on the small holder tubes to align the reflectors etc. I believe this was one of your ideas and works brilliantly. I think I will also use them for my narods in the spine this time - last time I just used thru holes and silicone to keep them from moving. All of my plastic tubes are press fit - the small pvc holder tubes into the larger pvc standoffs and the pvc standoffs into the ABS central spine. To do press fits with abs/pvc you need to make the holes 3-5 thousands of an inch smaller than the diameter of the tube. This requires a good selection of bits/cutters. I used forstner bits for the larger holes. I also used some keepers on the standoffs because I had to stretch some of the holes to get them to line up. This shouldn't be necessary if done properly. This time I will use a drill press and a fixture to ensure accuracy. I wish I had a milling machine again!
2011-06-28, 03:01 PM
I decided for the time being to eschew fiddling with making my own reflector rods from sheet aluminum for the GH10n3 SNAP under construction. I will go with Al foil tape wrapped over 5/16" dia fiberglass driveway marker rod, my original intent.
(See my album for more photos and description)
I have already worked out a way to attach a single continuous length of rod at every reflector location, without the foil being gripped by a hard material and without creating a stress riser at the point where the rod exits the holder. It took just a few minutes to work out how to wrap the foil around the rod, and even the first one was a keeper. I degreased the rod using alcohol. If the foil proves to be durable, this is a really quick and easy way to make reflectors. I do not know the pedigree of the foil tape I used. I bought it at a home center years ago, and it has no markings on the roll. More than five years ago I put a small tab of this tape on a vertical Al surface outdoors, exposed directly to the weather, and that sample shows no sign of degradation (still slick and shiny) or of coming unstuck. If I were starting from scratch, I would choose the special tape available at the home center that offers the highest quality adhesive (and highest cost). The edges of my tape had gotten damaged over the years, so I trimmed a quarter inch off of each edge, leaving Al foil 1-1/2" wide. Note that cutting fiberglass rod subjects you to injury from tiny sharp fibers.
2011-06-28, 05:26 PM
That looks cool! I haven't figured out a way to use them yet but there are also 1/8" x 1/2" fiberglass bars that are used to lock the end of chain link fencing. They are quite inexpensive (a couple bucks?) and are about 4 ft. long. Maybe wrapped with foil tape they would make some kick-butt reflectors.
2011-06-28, 05:51 PM
Unclesam and 2bits.
YES! That's the idea allright.
I was going to do something very similar with the 1/8 x 1/2 x 4or5ft long fibreglass "fence spreader rods" and AL or CU foil on one side.
Make the gapped / split reflectors like that with a continuous piece of fibreglass rectangular rod and 2 strips of foil.
I was going to cut the foil strips with an office paper shear. Maybe attach / tape the foil to long paper strips and then shear away thin long strips as reflectors. Could one even use household aluminum foil ? Very thin though.
I have 6 or so of those rods purchaced, and I have the CU foil in a roll (thin CU foil not easy to find in long enough lengths). It's CU shim stock (sort of expensive ... but I got it). But AL will work just as well I think. Cut AL strips and glue to rod with the correct gap. Then coat with protective coating ?
I think that will make great reflector rods for a GH.
Very interested to see how that sort of reflector construction will perform.
... if I ever get round to it myself too ...
Should work well I believe ...
2011-06-28, 09:30 PM
I will go with Al foil tape wrapped over 5/16" dia fiberglass driveway marker rod, my original intent.
If you check your local Lowes, one eight foot piece of 1/2" X 1/2" X 1/16" thick aluminum angle should be about the same price as two 4 ft fiberglass driveway marker rods. They would perform about the same as 1/2" rod (or 1.4142 X .5" = .707" diameter rods if turned on an angle. Turned on an angle, they could be easily fastened to pvc pipe tubes.)
2011-06-29, 09:04 AM
On the other hand, pvc tube with a thin coat of contact cement and then aluminum foil with a thin coat of contact cement then wrapped around the tube would do away with the need for any alum angle at all. But would it stand up to the elements?
2011-06-29, 10:02 AM
2bits, you used your home-made Al tubes for your active elements. Did you bend a tube into a zigzag shape, or did you fasten together short links of tubing at the corners, similar to what I have done using 1/4" copper tubing? If you used links, how did you fasten the corners to ensure electrical contact? After making a few of the needed reflectors by wrapping Al tape around fiberglass rods, I realized that the tape could be wrapped around smaller plastic rod to make links for active elements. The ends could be heated, pressed flat-ish, then drilled to make links. It may be that good electrical and mechanical connection at the corners could be made using Al pop rivets and Al washers. Degradation of the electrical performance of the corner connections with exposure to weather over time would be the question. My sample of the Al tape itself has remained smooth, slick and shiny after more that five years of direct exposure to the weather.
2011-06-29, 11:02 AM
I have a boatload of "unobtainium" that makes for brilliant antenas , even as a lump of molten slag :D
bet no one else has it ....:cool:
2011-06-29, 12:04 PM
cement then wrapped around the tube would do away with the need for any alum angle at all.
Heh, I meant using the aluminum angle instead of rod, not in addition too. :p
Turned on an angle, they could be easily fastened to pvc pipe tubes.
And I meant here, just attached to a stub of a pvc/fiberglass tube or rod.
Oddly 1/2" aluminum angle is the cheapest per ft in my area. Cheaper than 1/4" or 3/8" aluminum rod or even 1/2" flat aluminum , go figure.
I saw a few posts here on bending metals but I would like some tips. I am planning on heating some aluminium flat bar to build a Chireix Zig-Zag or SH. Heat will be via a propane torch. Anyone have any tips? Like heat until dull red and hammer gently. I plan to place the bar in my vice, heat and gently bend and tap on it. I don't have a jig. I have read that this unheated flat bar can be brittle given the near 90° bends. I would really like to have clean angles without compromising the metal. I have no idea of the temper or quality. It is stock 8' x 3/16" x 1/2" from Home Hardware.
Second question: With the same bar type I may also try a 6-whisker bow tie. All the posts talk about 8 or 10 gauge wire. Will the flat bar work without modification? Obviously the whiskers will be stacked flat and given its 1/2 profile will I need to adjust the separation or length? 8 gauge is 1/8" so this is 50% thicker and has a 7X larger cross section.
2011-06-29, 01:55 PM
Take a look at http://www.digitalhome.ca/forum/showpost.php?p=1187764&postcount=54
It is a post I made about making aluminum rod easier to bend by heating it with a propane torch. Hopefully it helps you out.
Wow absolutely superb. Thanks for the tips. I have some reading to do.
2011-06-30, 04:34 PM
An excellent tutorial hankcurt. I learned something and I have worked with aluminum as a welder/machinist. The difficult part about aluminum is that because it forms a very hard oxide on its skin (of which the melting temperature is much higher than the aluminum below) the whole piece can suddenly collapse into a puddle without any visible indicators.
2011-06-30, 04:42 PM
difficult part about aluminum is that because it forms a very hard oxide on its skin (of which the melting temperature is much higher than the aluminum below) the whole piece can suddenly collapse into a puddle without any visible indicators.
Yep, and all you need to demonstrate that effect is an empty aluminum beer/soda can and a propane torch (or a campfire or bar-b-que grill). :p
2011-06-30, 04:52 PM
2bits, you used your home-made Al tubes for your active elements. Did you bend a tube into a zigzag shape, or did you fasten together short links of tubing at the corners, similar to what I have done using 1/4" copper tubing? If you used links, how did you fasten the corners to ensure electrical contact?
I bent the angles on a sharp corner to the desired angle and then flattened them to the nominal diameter while holding the angle in a vise. Not pretty but effective. This also has the added benefit of work-hardening the aluminum so the corners become very stiff. No cracking or breaking to this point and it is easy that way to maintain the lengths of the zig-zag legs. I would think the fiberglass rods could be bent using heat or cut and re-bonded at a 90 degrees using chemicals or body-shop supplies.
2011-06-30, 06:30 PM
300ohm, one eight foot piece of 1/2" X 1/2" X 1/16" thick aluminum angle should be about the same price as two 4 ft fiberglass driveway marker rods., Cost is not the primary consideration for me in building an OTA antenna. How can you put a price on unfettered free access to reruns of Benny Hill? Anyway, who would expect to build their own tv antenna without investing a few thousand dollars in machinery and materials? One must also maintain a certain level of esthetics. Here at Do Little Farm, reflector rods, like pies, are round, not angledy. http://www.digitalhome.ca/forum/picture.php?albumid=797&pictureid=4224
My attraction to the fiberglass rods covered with metal tape is that there is but one connection to the framework at each reflector station. These rods are nearly perfectly straight, so if the framework is straight and plumb (and mine is), the reflectors will all be straight and parallel, and the gaps will be correct without having to fiddle with them. It remains to be seen if reflectors made in this manner will be suitable in the long run, but I do not think I have seen prettier. It was fairly easy to roll the tape onto the rods tightly and smoothly.They appear as if the rods have been given a really heavy chrome plating.
Today I ran across driveway markers in fiberglass that are true 1/4" diameter, and I now believe I could wrap those in metal tape. These were too costly, because they were supplied with a pointed metal stob that would be driven into the ground and had a threaded top to accept a threaded adapter on the bottom of the rod. Something for next time.
2011-06-30, 08:05 PM
Nice looking job unclesam. While I admire your dedication to esthetics, and am totally in agreement with you on your observations about pies and Benny Hill, here at the poor farm we have found it necessary to focus on cost as well as driving the economy onward. I do think that those rods will stand up though. Today I came back from a trip up to the Haliburton hills in Central Ontario where the antennas are big and plentiful. Many are older VHF yagis and suffering from neglect. I would venture to say that all most all of the broken, dangling or bent reflectors and directors are a result of the mounting brackets for those tubes letting go and starting the process of failure.
2011-07-01, 01:40 PM
This is how reflectors made by wrapping Al tape around 5/16" dia fiberglass rod are made into preassembled modules that can be snapped into the antenna's frame (details in my photo album). Squeezing the rubber grommets between the caps and the ends of the pipe forms a very tight but resilient grip on the rod and provides a watertight seal at the rod and at the inner face of the caps. I do not intend to put weep holes in these assemblies. I also will not cement the assemblies into the frame until the antenna frame has been attached to the mast at the time of final installation. Carrying the reflectors separately will make it easier to move the antenna around in the meantime for preliminary reception tests, photo shoot, etc.
Enclosing the rods inside the short CPVC pipe will have some, unquantifiable, effect on the performance of the antenna. However, I used the same mounting system on my first GH10n3 reflectors, and that antenna provides extremely good reception in a location where virtually none would be expected.
2011-07-01, 08:36 PM
unclesam, I used this mounting design of yours for my reflectors also except for the grommets. My tubes can be wound a little to a smaller diameter and then allowed to spring back to size once into position. This locks them securely in the drilled end caps. I didn't worry about a weather proof seal since the tubes themselves can't be sealed in their present incarnation. Perhaps for me weep holes would have been prudent.