Building XGH - Canadian TV, Computing and Home Theatre Forums

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post #1 of 24 (permalink) Old 2012-03-02, 01:04 PM Thread Starter
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Building XGH

So I think I'm finally ready to start building an XGH. 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?
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post #2 of 24 (permalink) Old 2012-03-02, 06:20 PM
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Quote:
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.

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post #3 of 24 (permalink) Old 2012-03-02, 11:55 PM
 
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JED posted a shorter (not as tall) version XGH here
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post #4 of 24 (permalink) Old 2012-03-03, 01:16 AM
 
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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
Get Build Measurements from NEC data with 4nec2

here's the model that nikiml pointed to rescaled to 479 MHz
Code:
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.

my gain reports and models are here

Last edited by GHZ24; 2012-03-03 at 02:42 AM. Reason: add
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post #5 of 24 (permalink) Old 2012-03-05, 01:44 PM Thread Starter
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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?
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post #6 of 24 (permalink) Old 2012-03-05, 04:04 PM
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Quote:
300ohm: height relative to what?
The middle, which is zero. Positive values go up from the middle and negative values go down.

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post #7 of 24 (permalink) Old 2012-03-05, 11:41 PM
 
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Quote:
Have you tried putting that into 4nec2?
I used 4nec2 to scale the original 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?

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post #8 of 24 (permalink) Old 2012-03-06, 07:11 PM Thread Starter
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GHZ24: I don't know what I did wrong on mine, but your file worked like a champ. I'll take measurements from that.
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post #9 of 24 (permalink) Old 2012-03-08, 03:57 PM Thread Starter
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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?
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post #10 of 24 (permalink) Old 2012-03-08, 06:27 PM
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Quote:
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.

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post #11 of 24 (permalink) Old 2012-03-08, 09:40 PM Thread Starter
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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.
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post #12 of 24 (permalink) Old 2012-03-08, 10:01 PM
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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.

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post #13 of 24 (permalink) Old 2012-03-08, 10:04 PM Thread Starter
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Yes, solid core.
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post #14 of 24 (permalink) Old 2012-03-08, 10:22 PM
 
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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.

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post #15 of 24 (permalink) Old 2012-03-08, 10:43 PM Thread Starter
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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...
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