This is my first post here, signed up this morning with much drama… ;-) To make a long story short, I’m building a GH.

The design is 95% complete. Every specified dimension and spacing in the GH plans will be accurately adjustable.

The ‘wall’ is made of money… With off-the-shelf components, building this thing is gonna’ cost 150 bucks US!, [give or take], and it’s not even gold plated…;-) I recently said; ‘Ha!!! Impossible just takes longer’. I should have added; ‘and is hugely more expensive!’. Needless to say, I’m researching alternate materials.

The biggest single hit is a block of machineable insulating material 1 ½ inches x 6 inches x 20 inches long. I’ve priced PVC and Garolite to name a couple and for the piece I need it runs from $80 to $100… [McMaster-Carr] Any suggestions for less expensive material/sources?

Can I use brass rather than copper for the elements?

Lastly, how important is the diameter of the elements? The GH plans call for .125 material. Would I be in trouble if I used .155 material? What if I mixed the two diameters on a single element?

The upside of this grand plan is that once it’s built you could easily configure it to any GH variant or tweak you wanted to try out.

Anyhow, thanks in advance for any words of wisdom…

Best,
Chip

The ‘wall’ is made of money… With off-the-shelf components, building this thing is gonna’ cost 150 bucks US!,
I’ve priced PVC and Garolite to name a couple and for the piece I need it runs from $80 to $100… [McMaster-Carr]
Heh, what in the world are you building ???? My plans in the sticky above should only run you $25 or less buying everything off the shelf at Lowes or Home Depot. For the piece of machinable plastic 1 ½ inches x 6 inches x 20 inches long, scrap quality plastic composite decking material glued together should fit the bill. Just use the good stuff that has more plastic than wood flour.

Can I use brass rather than copper for the elements?

Lastly, how important is the diameter of the elements? The GH plans call for .125 material. Would I be in trouble if I used .155 material? What if I mixed the two diameters on a single element?

Brass is OK, but not as good as copper or aluminum, and is usually more expensive. But dont mix two different sizes on the elements. .155 diameter is OK too. Anything from .08 to .375 inch diameter are typical UHF sizes for elements.

building this thing is gonna’ cost 150 bucks US!Hi Chip and welcome here. I second 300ohm on that - your use of machineable plastic sure spikes the budget! :eek:

Hey 300 & stampeder… Always good to hear from youse’ guys!

I kinda’ sorta’ dreamed this thing up without checking prices… silly me ;-).

The basic mast is a piece of aluminum ‘Unistrut’ [trade name I think]. Go to McMaster-Carr dot com and key ‘unistrut’ into the search engine. This stuff will give you the ability to adjust the vertical spacing to anything you want.

The ‘block of insulating material’ with a little lightweight machining and sliced up into 1 inch pieces is the standoffs. If you’re good, [better than me!] it could be done on a table saw. 300: Inspired tip on the ‘composite decking’!!! Could you come up with brand names or something so I can identify the ‘good stuff’?

The question about varying the element diameters has to do with making the element lengths adjustable… Think rabbit ears. If it needs to be copper then so be it… Just a bit less convenient to tweak element lengths.

This is a real friendly place… Thanks!!!

Best,
Chip

The question about varying the element diameters has to do with making the element lengths adjustable… Think rabbit ears. If it needs to be copper then so be it… Just a bit less convenient to tweak element lengths.

This is a real friendly place… Thanks!!!

Best,
Chip

Chip,

I've emailed Barack, to let him know you are doing your bit, to get money circulating in this troubled economy with your GH project... so you should be getting an accommodation letter from the White House, soon after the inauguration :p

Seriously, it sounds that you are making an important contribution to the GH projects in making a "variable" mounting structure.... that's great !! I'll be very interested in seeing your pics.

Past modeling has shown that the conductivity of the elements, Alu, Copper, steel etc, is not a very significant factor, so from a cost point of view, the cheapest is fine. If you are planning on a long-term outdoor installation ( say >10 years), then corrosion factors should be your guide, in choosing elements.

300: Inspired tip on the ‘composite decking’!!! Could you come up with brand names or something so I can identify the ‘good stuff’?

I found the Monarch brand samples at Lowes were very good. Mostly I would look at the cut end of the composite decking, and if I saw solid plastic all the way, instead of plastic and wood chips, it should be very good. Of course, check it with an ohmmeter. For indoor use, the cheaper stuff should be fine too. One disadvantage is that its quite heavy, heavier than wet wood, heh.

The question about varying the element diameters has to do with making the element lengths adjustable… Think rabbit ears. If it needs to be copper then so be it… Just a bit less convenient to tweak element lengths.

OK, I see what youre thinking about. Those small differences in diameters on rabbit ears are OK. It wont follow the model, but will still work fine. In fact, why not use a bunch of old rabbit ears or other old radio antennas ? 8 sets (16 total elements) would do it. Flatten out the ends, drill a small hole, insert a wing nut and bolt. Then it would be adjustable and folding.
The only thing, the compressed length of the shortest rabbit ears Ive found are 7 inches.

The ‘block of insulating material’ with a little lightweight machining and sliced up into 1 inch pieces is the standoffs.
Im still confused about why the 1 inch plastic pieces have to be 1 1/2 inches thick ? The plastic from an HDPE cutting board, 1/4 to 1/2 inch thick, found in kitchen depts, is cheap as are plexiglass pieces.

Overall, $150 is a little pricey to make an antenna to experiment with. Modeling with software is much easier, heh.

Plastic lumber… I think I might be back in the game! Thanks 300...! Check out ‘plasticlumberyard dot com’. Looks like I can get what I need for 10 bucks or so, which puts the whole thing back down in the doable range. Maybe I won’t need help from the Obamatron after all… However if a check arrives, I’ll cash it ;-)

The plastic needs to be at least 1 ½” thick because it needs a channel milled in the back to accurately fit over and clamp to the unistrut at exactly a 90 degree angle and still be rigid enough to support the elements. Even thicker would be better. At this point the whole plan is pretty much in my head, but I can do up a little drawing and send it along as soon as I have enough posts to do attachments.

The telescoping feature… I’ve found that 1/8th inch brazing rod fits perfectly inside 5/32 brass tube, [.155 OD]. I’m pretty sure that the same thing works with copper but that’s another cost issue. I’m trying to stay as true to the computer models as possible so if mixing diameters on a single element changes things a lot, that feature will have to go away.

To be honest I haven’t really much considered ‘weatherability’, however it seems like the way it’s shakin’ out, it’ll be pretty good that way. I think that I’m most likely gonna’ step up for the copper. The weak point corrosion-wise will be the telescoping part of the plan.

Truth be told, when I get it done I’ll have no way to test it. I’ll have to hook up with one of you guys to do a proper test to see if it works. I have neither the skills nor the equipment. My current antenna setup is seriously lacking and as you know, with DT either you get it perfect or not at all. Even so, there are no more channels for me to get… Until I get to Vancouver of course! ;-) My hope is that if it actually works at all, and I can keep real close to the computer models it will provide a test bed for the applied researcher to compare the computer modeled numbers with the real numbers without having to build a whole new one every time there’s a new variant or tweak.

The real bottom line is that I find this kind of thing just a boatload of fun…

Now I gotta’ go shag some parts and go sweet-talk a machinist friend of mine…

Chip

Well, things are progressing. The plastic arrived and I’m in the process of fabricating the standoffs. Getting ready to order the reflector/array elements… Which leads to a question.

In post #7 of this thread;

http://www.digitalhome.ca/forum/showthread.php?t=96483

Autofils indicates that the element diameter is 1/8th inch, however on Mr. Davis’ page it seems to indicate that the ‘D’ parameter is ¼ inch..

What am I missing?

Best,
Chip

What am I missing?

Nothing. Either design will work with about 16ga to 3/8 inch wire with only minor performance differences. The thicker stuff is more durable outdoors, but costs more and is harder to work with.

You can get 1/4" copper tubing from the plumbing section of Home Depot. It comes in 20' lengths and costs around $15. I think this should work almost as well as solid copper and be weather the elements.
harryw

Yep, and it has even dropped in price to where the 1/4 OD inch copper tubing at Home Depot is less than the #6 solid copper wire is at Lowes. Its just a little bit harder to straighten. They also sell it in 10 ft rolls (enough for a regular SBGH) for less than $8.

Thanks for the input guys. I haven’t quite pulled the trigger on the element material, but my current favorite is ¼ inch .014 wall aluminum tube, [7/32 for the telescoping part] from McMaster Carr… about a buck a foot.

Of course the budget is out the window…[altho’ I have trimmed it quite a bit.]

I would understand if you all were to view me as somewhat of a dilettante… [I prefer ‘eccentric’ ;-)], but I will finish this thing, and it will be glorious…

Best,
Chip