: Building XGH


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PopeFelix
2012-03-02, 02:04 PM
So I think I'm finally ready to start building an XGH (http://www.jedsoft.org/fun/antennas/dtv/xgh.html). Based on the design at the provided link, I have a couple of questions:


Is it safe to assume that all the angles of the bends in the driven elements, save the top and bottom, are 90 degrees?
What do the z-sub-n numbers represent?
What do the delta-z-sub-n numbers represent?


If I've calculated things correctly (I modified the design from 615 MHz to 479 MHz because I want to use this to catch UHF channel 15) I have a vertical size of 3.1 m, and a horizontal size of 3.2 m. I'll need 9m or so of wire.

Anyone done this before? :)

300ohm
2012-03-02, 07:20 PM
Is it safe to assume that all the angles of the bends in the driven elements, save the top and bottom, are 90 degrees?
No, thats why the "z" figures. Z is the height distance measurement. Delta Z is the change in height.

nikiml
2012-03-03, 12:55 AM
JED posted a shorter (not as tall) version XGH here (http://www.digitalhome.ca/forum/showpost.php?p=836346&postcount=26)

GHZ24
2012-03-03, 02:16 AM
What scaling factor did you use? 1.284 ? because I get ~ 114 inches or about 2.9 meters (rescaling the taller first model you posted a link to )

and 83.375 inches or about 2.1 meters for the rescaled height of the model
nikiml posted a link to.

Edit:

Here's a short thread about getting measurements from models
http://www.digitalhome.ca/forum/showthread.php?t=107457

here's the model that nikiml pointed to rescaled to 479 MHz
CM
CE
GW 1 17 0 -3.025928 0 0 3.02592798 0 0.125
GW 2 43 0 -3.025928 0 0 -13.029061 10.0031688 0.125
GW 3 43 0 -3.025928 0 0 -13.029061 -10.003169 0.125
GW 4 43 0 3.02592798 0 0 13.0290614 10.0031688 0.125
GW 5 43 0 3.02592798 0 0 13.0290614 -10.003169 0.125
GW 6 37 0 -13.029061 10.0031688 0 -4.3225001 18.7097504 0.125
GW 7 37 0 -13.029061 -10.003169 0 -4.3225001 -18.70975 0.125
GW 8 37 0 13.0290614 10.0031688 0 4.32250006 18.7097504 0.125
GW 9 37 0 13.0290614 -10.003169 0 4.32250006 -18.70975 0.125
GW 10 39 0 -4.3225001 18.7097504 0 -13.439638 27.8268581 0.125
GW 11 39 0 -4.3225001 -18.70975 0 -13.439638 -27.826858 0.125
GW 12 39 0 4.32250006 18.7097504 0 13.4396381 27.8268581 0.125
GW 13 39 0 4.32250006 -18.70975 0 13.4396381 -27.826858 0.125
GW 14 33 0 -13.439638 27.8268581 0 -5.646112 35.6203337 0.125
GW 15 33 0 -13.439638 -27.826858 0 -5.646112 -35.620334 0.125
GW 16 33 0 13.4396381 27.8268581 0 5.64611197 35.6203337 0.125
GW 17 33 0 13.4396381 -27.826858 0 5.64611197 -35.620334 0.125
GW 18 25 0 -5.646112 35.6203337 0 -11.713366 41.6875876 0.125
GW 19 25 0 -5.646112 -35.620334 0 -11.713366 -41.687588 0.125
GW 20 25 0 5.64611197 35.6203337 0 11.7133658 41.6875876 0.125
GW 21 25 0 5.64611197 -35.620334 0 11.7133658 -41.687588 0.125
GW 22 17 0 -11.713366 41.6875876 0 -17.79346 41.6875876 0.125
GW 23 17 0 -11.713366 -41.687588 0 -17.79346 -41.687588 0.125
GW 24 17 0 11.7133658 41.6875876 0 17.7934597 41.6875876 0.125
GW 25 17 0 11.7133658 -41.687588 0 17.7934597 -41.687588 0.125
GW 26 35 -2.294432 -6.333305 -40.0429 -2.294432 -17.58342 -40.0429 0.125
GW 27 35 -2.294432 6.3333047 -40.0429 -2.294432 17.58342 -40.0429 0.125
GW 28 35 -2.294432 -4.154706 -24.37669 -2.294432 -15.73714 -24.37669 0.125
GW 29 35 -2.294432 4.1547055 -24.37669 -2.294432 15.737139 -24.37669 0.125
GW 30 37 -2.294432 -2.439322 -13.05156 -2.294432 -14.42261 -13.05156 0.125
GW 31 37 -2.294432 2.439322 -13.05156 -2.294432 14.422606 -13.05156 0.125
GW 32 71 -2.294432 -1.187169 -4.169108 -2.294432 -23.98345 -4.169108 0.125
GW 33 71 -2.294432 1.1871692 -4.169108 -2.294432 23.983452 -4.169108 0.125
GW 34 71 -2.294432 -1.187169 4.1691076 -2.294432 -23.98345 4.1691076 0.125
GW 35 71 -2.294432 1.1871692 4.1691076 -2.294432 23.983452 4.1691076 0.125
GW 36 37 -2.294432 -2.439322 13.051557 -2.294432 -14.42261 13.051557 0.125
GW 37 37 -2.294432 2.439322 13.051557 -2.294432 14.422606 13.051557 0.125
GW 38 35 -2.294432 -4.154706 24.376689 -2.294432 -15.73714 24.376689 0.125
GW 39 35 -2.294432 4.1547055 24.376689 -2.294432 15.737139 24.376689 0.125
GW 40 35 -2.294432 -6.333305 40.042905 -2.294432 -17.58342 40.042905 0.125
GW 41 35 -2.294432 6.3333047 40.042905 -2.294432 17.58342 40.042905 0.125
GS 0 0 0.0254
GE 0
LD 5 0 0 0 24900000
GN -1
EK
EX 0 1 9 0 1 0 0
FR 0 0 0 0 479 0
RP 0 60 73 1001 0 0 3 5
EN


It does have a nice pattern.

PopeFelix
2012-03-05, 02:44 PM
GHZ24: Yes, I used a scaling factor of 1.284 (615/479). I'll check my math, but thanks for posting the scaled version of the shorter XGH. Have you tried putting that into 4nec2? When I tried it with my scaled version, it came up with some kind of error; I don't recall what offhand.

300ohm: height relative to what?

300ohm
2012-03-05, 05:04 PM
300ohm: height relative to what?
The middle, which is zero. Positive values go up from the middle and negative values go down.

GHZ24
2012-03-06, 12:41 AM
Have you tried putting that into 4nec2? I used 4nec2 to scale the original (http://www.digitalhome.ca/forum/showpost.php?p=836346&postcount=26) so yes I also ran the model at 479 and got ~18.3 dBi and beamwidth of 28 degrees the AGT is a little off at 1.02 (.09 dBi) but that wont effect the measurements you get from it.

Except the wire radii which are rescaled along with the other dimensions.

I used the geometry editor to rescale just select all wires then edit>resale wires I did have to change the FR card from 585 to 615 cause that's where geo edit gets it's "start frequency" from
Can you open the one I posted?

PopeFelix
2012-03-06, 08:11 PM
GHZ24: I don't know what I did wrong on mine, but your file worked like a champ. I'll take measurements from that.

PopeFelix
2012-03-08, 04:57 PM
I've got my measurements, and am ready to start assembling materials. I'm thinking PVC for the frame, of course, but should I use aluminum or copper for my driven elements and reflectors?

300ohm
2012-03-08, 07:27 PM
I'm thinking PVC for the frame, of course, but should I use aluminum or copper for my driven elements and reflectors?
Use the cheaper gray electrical pvc pipe, its UV resistant.

Gain wise, not a real measurable difference between aluminum and copper, so use what is cheapest and/or most available in your area.

PopeFelix
2012-03-08, 10:40 PM
How much does insulation on the wire matter? I can get #4 aluminum wire from the hardware store for $0.49/ft, but it's insulated, and I really don't relish the thought of stripping off all that insulation.

300ohm
2012-03-08, 11:01 PM
Solid core ? The insulation on the wire changes its velocity factor. On a very narrow band antenna like the XGH, I would remove the insulation. Its easy to do by holding a utility knife on an angle to the wire and slicing away from you.

PopeFelix
2012-03-08, 11:04 PM
Yes, solid core.

GHZ24
2012-03-08, 11:22 PM
Personally I like copper for elements due to dissimilar metals.
Most baluns are brass ends/screws on copper wire and copper to copper is easy to solder.

Aluminum is lighter and cheaper than copper and used on almost all commercial TV antennas but those commercial antennas always seam to corrode at the point where the balun connects first.

I think there is a thread about dissimilar metals here somewhere.

But if you only connect (that is physically touch) same metals then you don't have to worry about it.

I'm a fanatic though. A lot of people use aluminum with no problems.
300ohm is right strip the wire.

PopeFelix
2012-03-08, 11:43 PM
What if I were to tin the ends of the copper wires on the balun with solder? I've read that can help reduce the amount of galvanic corrosion. I'd have to join the tinned ends to the aluminum elements with some kind of strap, I suppose, rather than soldering them...

300ohm
2012-03-08, 11:54 PM
I'd have to join the tinned ends to the aluminum elements with some kind of strap, I suppose, rather than soldering them...
Yes, use bolts and nuts. For aluminum, use aluminum nuts and bolts, first choice but theyre on the weak side so you have to be delicate. Second choices would be to use galvanized or stainless steel nuts and bolts with aluminum.

For copper use copper or brass nuts and bolts.

There are dielectric coatings you could use, but theyre so pricey for a small tube, its much cheaper to use the right nuts and bolts.

GHZ24
2012-03-09, 01:55 AM
Like stainless better than galvanized (zinc) for aluminum.

Again just my preference.

For copper use copper or brass nuts and bolts.

You don't like solder ?

300ohm
2012-03-09, 02:17 AM
You don't like solder ?
Its a little tough to solder when you up more than 20 ft in the air, heh. (Ive done it though :o )

PopeFelix
2012-03-09, 04:18 PM
300ohm: you can always clean your tip on the cuff of your pants... :)

I think I'm going to go with copper, actually - 1/4" copper tubing. Hopefully the local copper thieves won't nab it.

I'll post a detailed build plan once I have one. :)

PopeFelix
2012-03-09, 06:40 PM
One more thought I had: what about wind load? I intend to mount this on a rooftop tripod on top of my house; I don't want to rip a hole in my roof, as it's a rental.