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Discussion Starter #1 (Edited)
I was just wondering how the SBGH GH10 curved reflector worked out, 300ohm. I've been going for some deep fringe channels all 2 edge or worse. I'm especially interested in channel 15 which I can get consistently with mild tropo but otherwise I get dropouts. I built a Mclapp with 11.5" whiskers and 11" spacing and it is marginally better that my 91xg. Since I have a heavy duty Rohn mount on the roof from a 4ft satellite install I may try a DBGH Curved reflector. Did you ever try that? Since the highest channel I cannot get reliably is at 41 (comes in most of the time especially at night) and the ones that come in intermittently are 36 and 20, perhaps the huge curtain antenna you modeled and balm tried to build would make more sense? Obviously the larger reflector for the SBGH GH would make more sense according to your gain charts. A little tropo last night and all the Buffalo stations came in solidly with the Mclapp. I have a Winegard yagi on a tower about 50 feet up that does fine with all the Erie stations to the north.

 

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Discussion Starter #2 (Edited)
300ohm curtain quad

It has been a month or so since my last post. So far no replies :( I have since spent a fair amount of time browsing this site. I am interested in ultra high gain for low uhf, particularly channel 15. I was seriously considering building a DBGH curved reflector GH19 similar to 300ohm's SBGH GH10 (Hey, someone has to try it out). The feedline ganging the 2 bays looks a little more complicated. I wasn't sure of the ideal length though I have read 2x wavelength - .2x wavelength would work. Wasn't sure if that is what a GH19 would default to when ganging 2 GH10's using a common upper/lower reflector support. The curtain quad, however, looks like an easier build and since the station, while tropo is frustratingly close, a larger aperture may help. Unfortunately, while the reflector seems fairly straightforward as is the 4.5" reflector to element spacing, the dimensions of the quad array are unclear to me. I've tried to figure out the nec modelling software but that has been a little of a challenge so far. If anyone could tell me the dimensions of the quad array and the details of the elements where the balun attaches I would be most appreciative. I have eighth inch copper rod to cut and braze for the array. I wonder if that is OK.
 

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It has been a month or so since my last post. So far no replies
Oops, sorry about that. I must have skipped over it somehow. Yes, I built a SBGH 10 with the curved mesh reflector. I works fine, but its large, heh. A DBGH GH curved mesh reflector would be a monster.

I have eighth inch copper rod to cut and braze for the array. I wonder if that is OK.
Yes, that would be great but pricey. For curtain quads, you may want to consider using galvanized fence wire, sold in the fence dept at Home Depot or Lowes. The gain is only going to be a bit less, but its cheaper and stronger than copper.
Since you have brazing equipment, give the curtain quad a shot.

I've tried to figure out the nec modelling software but that has been a little of a challenge so far. If anyone could tell me the dimensions of the quad array and the details of the elements where the balun attaches I would be most appreciative.
For getting the dimensions, just follow my easy directions here :
http://www.digitalhome.ca/forum/showthread.php?t=107457

The balun connection point is where the wire with the red ball on it is at. (that wire is not a real physical wire. Its a source wire for modeling purposes)
 

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Discussion Starter #4
Thanks

Thanks for the prompt reply. I'll let you know how the curtain quad compares to the 4 bay McClapp I'm using now.
 

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Discussion Starter #5
8 Gauge Aluminum

I found an old unused length of RatShack 8 gauge aluminum ground wire in the garage. I assume this would be ok for my curtain quad array?
 

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Yes, thats good antenna material too. But unless you have specialized heliarc welding equipment, you cant braze it together for a curtain quad.
I think it would be too thin for use with the alumi-rod stuff.
 

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Discussion Starter #7
1/8" copper rod

I have some of this that I got to build the McLapp. I brazed the whiskers to the phasing lines. Maybe I'll just use that since I'm new to brazing. I just used mapp gas and brazing rod to braze the McLapp. I went to Tractor Supply today. I wasn't sure what is galvanized wire the curtain quad was modeled for. I found some fencing wire but it was awful thin. If well supported can aluminum be soldered? Only have experience working with copper.
 

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I found some fencing wire but it was awful thin. If well supported can aluminum be soldered?
I think the fencing wire you were looking at in Tractor Supply was for electrical fencing, which now a days, is pretty thin. The 9 gauge stuff I was talking about is sold at Lowes and Home Depot, and is used with chain link fencing.

Aluminum can be brazed using the alumarod type stuff.
http://www.aluminumrepair.com/aluminum_repair.asp
Its also sold at Harbor freight in small pricey packets.
The trouble is, with 8 gauge wire, it may puddle and melt before you can attach a piece to it, making the job very tricky to do. Aluminum doesnt have a large temperature bandwidth to work with. One minute its solid and with more heat, it just colapses. Try putting the mapp gas on an empty beer can to see what I mean, heh.

I think the 9 gauge fencing wire with regular cheaper brazing rod would be the cheapest way to go for a curtain quad. I believe the 9 gauge fencing wire at Home Depot is less than $20 for a 170 ft coil of it.

But if youre building the 13 element curtain quad, and already have the copper rod, then go ahead and use it. (I just personally would save the copper for the GHs as copper is back up to around the $4 / lb range http://www.metalprices.com/ )
 

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if making all the 90 deg joints yourself, i think you will find it very difficult to maintain stable joints, thus the method of joining the wires becomes very important, as well as extensive supporting from the framing
 

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Discussion Starter #12 (Edited)
13 Element Curtain Quad

I have all the pvc for the frame cut out. It's, uh, BIG. The idea of simple 1/2" pvc painted sounds like a good idea. Standard 5/8" dowels fit inside very snugly. I was going to use larger pvc but I couldn't find dowels that would fit snugly. With the dowels inserted it should be quite strong especially with 4 horizontal supports to hold the weight of the mesh. The main structural elements of the antenna frame form a rectangle that is only 36" x 76". Like balm, I plan to attach the mesh on the back. My plan calls for 12 stubs to support the quad array but based on balm's comments I may add a few more (1/2" tees are cheap). The local HomeDepot didn't have the galvanized wire so I have to pick it up tomorrow from a different store. My plan is to drill a tiny hole in the tension wire at the junctions and tie and wrap them with short lengths of thin fencing wire prior to brazing. Thanks for the tutorial on getting 4nec2 to work to check the wire lengths, 300ohm, and for your constructive (pun intended) comments balm. If I have time this weekend I may learn how to run the optimizer. The curtain quad you modeled, balm, is actually not that much larger. Maybe I should have tried that instead. The next task should be passing the WAF.
 

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Standard 5/8" dowels fit inside very snugly.
Putting some polyurethane construction glue in the pipe before inserting the dowels will snug it up even more as the polyurethane construction glue expands as it dries. :p Woodworking polyurethane glue does that too, but costs more than the construction stuff.
Polyurethane glue sticks to pretty much anything, as Ive used it to repair my sport type shoes at the rubber to leather contact points, heh.
My plan is to drill a tiny hole in the tension wire at the junctions and tie and wrap them with short lengths of thin fencing wire prior to brazing
Sounds good. :p

If I have time this weekend I may learn how to run the optimizer.
Before doing that, it would be worthwhile to you to explore all the great features of Geometry Edit and the Build feature, ie build and copy and paste and rotate and rescaleing and resegmentation etc of wires. Its a very powerful tool for free hand design of any antenna that you could think of, given the NEC2 engine limitations, which in designing a practical vhf/uhf antenna, arent limitations at all, heh.
 

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Discussion Starter #14
Galvanized Fence Wire

I hear you on the price of copper but have you ever tried to work with that galvanized tension wire? I'll pay a few bucks extra for gauge 4 copper which is sold by the foot at Home Depot! I have more experience brazing copper from building my McLapp. If I read the nec file correctly that is what the model calls for anyway.
 

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Discussion Starter #16
Completed!

I finished the curtain quad. Just got finished installing it on the roof. I couldn't find the camera to post a photo but will as soon as I do. Channel 15 may or may not be slightly improved compared to the McLapp. The McLapp had usable gain on channel 12. The curtain quad doesn't. It would probably help if I could find a tilting rotor to install it on since angling my 91xg did improve reception considerably. Despite the drop off at higher frequencies channel 50 comes in fine without pixelation. The DTVPal signal strength is a little lower than the McLapp (11.5" whiskers at 11" spacing) for channel 5. 22 and 24 are maybe a smidgen higher although they were 96+ on the McLapp anyway. I lost reliable channel 41 reception with the curtain quad which came in with the McLapp.
 

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It would probably help if I could find a tilting rotor to install it on since angling my 91xg did improve reception considerably.
The curtain quad does have a much narrower beamwidth than a 4 bay, so aiming it properly is much trickier.
 

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Discussion Starter #18
Curtain quad.

300ohm, I just thought you might like to know that the curtain quad works fairly well. I was able to watch PBS channel 15 this evening at a distance of 91 miles despite my living in a hole with no tropo at all tonight according to dxinfocenter.com When I get back after Thanksgiving I'm going to figure out a way to tilt it. Perhaps even with an old c band actuator.
 
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