Copper Tube vs. Wire for GH? - Canadian TV, Computing and Home Theatre Forums

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post #1 of 16 (permalink) Old 2008-04-21, 12:40 AM Thread Starter
 
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Copper Tube vs. Wire for GH?

I have a couple of questions.
  • Does the wire have to be bare? For example, could I use home wiring without stripping the insulation?.
  • Could you use copper tape on a window? Or would the capacitance throw the antenna out of whack?
  • If the window was a few degrees off, could you "steer" the reception lobes by altering the dimensions of the elements?

Last edited by stampeder; 2008-11-18 at 10:51 AM. Reason: post moved to this thread
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post #2 of 16 (permalink) Old 2008-10-03, 01:59 PM
 
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Copper Tube vs. Wire for GH?

I haven't been keeping up with the GH threads, but I've been doing a bunch of modelling & building on my own. One idea which I had turned out to be a dead end as to use 1/4" bendable copper tube for the active element. I was very surprised when the performance was significantly worse than the #10 steel wire I was using.

I've since figured it out, and confirmed it via modelling - curves instead of corners. Rather than kinking the tube at the 90' angles, I used a spring type pipe bender which kept the tube smooth but also limitted the radius of the curve. This significantly changes the current flows in the corners along with the overall dimensions..

Although I revised the model to account for the curves, I just couldn't get the performance I wanted.

So copper tube or pipe is probably a good way to improve a Yagi-Uda or other antennas with straight elements, but not such a good idea for antennas with bends - use wire.
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post #3 of 16 (permalink) Old 2008-10-04, 12:57 PM
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Quote:
One idea which I had turned out to be a dead end as to use 1/4" bendable copper tube for the active element. I was very surprised when the performance was significantly worse than the #10 steel wire I was using.
I actually noticed something similiar with Autofils GH10 model. The larger tubing, 5/16 inch, didnt perform as well as #6 or #10 copper with the screen reflector. Did you model copper wire ? Autofils did an analysis of using different metals in the Gen2 thread.

How did you model the curves ? With many many segments like I do ? Very tedious, heh.

On another note, Im building a 40inch by 40inch swept reflector 4 bay bow-tie antenna with a 14 inch element to reflector spacing for my Baltimore stations. My Baltimore stations will be 38-49 UHF and 11 and 13 VHF. Unlike the GH design, the bowtie with a large reflector and spacing gets about 6+ db on VHF-Hi, so its a better single antenna solution for my Baltimore stations. Im also attaching the mesh to the reflector like Darkonus did in his first build, ie cutting the mesh larger and using the end wires to wrap around the pvc pipe. With this method, not only do I save on cable ties, but I can tweak the mesh like a guitar, making the wires very tight and straight. Ive done some partial modeling on it, using 1 inch squares instead of circles, and there seems to be little to no effect, maybe even some tiny gain, by wrapping the wires around the pipe. (More modeling analysis needs to be done on it when I find time, heh).

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post #4 of 16 (permalink) Old 2008-10-04, 06:11 PM
 
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Quote:
Originally Posted by 300ohm View Post
How did you model the curves ? With many many segments like I do ? Very tedious, heh.
I use GA and GM tags for curves.
Code:
CM Single Bay Grey-Hovermann with split reflector
CM 4nec2 model created & optimized by Eric Ball
CE
SY lambda = 0.37758	'794 MHz
SY end=0.135	'end wire length
SY leg=0.140, l2 = leg / sqr(2)	'middle wire length
SY main=0.066, m2 = main / sqr(2)	'main wire length
SY nleg = int ( end / lambda * 40 + 0.5 )	'number of segments in leg wires
SY nend = int ( end / lambda * 40 + 0.5 )	'number of segments in end wires
SY nmain = int ( main / lambda * 40 + 0.5 )	'number of segments in main wires
SY rad = 0.035, r2 = rad / sqr(2)	'90 degree bend radius
SY nrad = int ( rad * pi / lambda * 10 + 0.5 )	'number of segments in 45 degree bend
SY gap = 0.0254, g2 = gap/2	'feedpoint/reflector gap 1"
SY rwidth=34.5in, rw2 = rwidth / 2	'total reflector width 34.5"
SY rheight=48in, rh2 = rheight / 2	'total reflector height 48"
SY nrw = int ( (rw2-g2) / lambda * 5 ) + 1	'number of patches in reflector half width
SY nrh = int ( rheight / lambda * 5 ) + 1	'number of patches in reflector half height
SY rdepth=4.125in	'reflector offset
SY rgap=0.5in, rg2 = rgap/2	'reflector gap
GA	1	nrad	rad	0	45	0.003175
GM	0	0	0	0	-90	0	rad+g2	0	1
GW	2	nmain	0	g2+rad-r2	r2	0	m2+g2+rad-r2	m2+r2	0.003175
GA	3	2*nrad	rad	-45	45	0.003175
GM	0	0	0	0	90	0	m2+g2+rad-2*r2	m2+2*r2	3
GW	4	nmain	0	m2+g2+rad-r2	m2+3*r2	0	g2+rad-r2	2*m2+3*r2	0.003175
GA	5	2*nrad	rad	-45	45	0.003175
GM	0	0	0	0	-90	0	rad+g2	2*m2+4*r2	5
GW	6	nmain	0	g2+rad-r2	2*m2+5*r2	0	l2+g2+rad-r2	l2+2*m2+5*r2	0.003175
GW	7	nend	0	l2+g2+rad-r2	l2+2*m2+5*r2	0	end+l2+g2+rad-r2	l2+2*m2+5*r2	0.003175
GX	7	011
GW	99	3	0	-g2	0	0	g2	0	0.003175
SM	nrw	nrh	-rdepth	-rw2	-rh2	-rdepth	-rg2	-rh2
SC	0	0	-rdepth	-rg2	rh2
SM	nrw	nrh	-rdepth	rg2	-rh2	-rdepth	rw2	-rh2
SC	0	0	-rdepth	rw2	rh2
GE	0
LD	5	1	0	0	58000000
LD	5	2	0	0	58000000
LD	5	3	0	0	58000000
LD	5	4	0	0	58000000
LD	5	5	0	0	58000000
LD	5	6	0	0	58000000
LD	5	7	0	0	58000000
LD	5	8	0	0	58000000
LD	5	9	0	0	58000000
LD	5	10	0	0	58000000
LD	5	11	0	0	58000000
LD	5	12	0	0	58000000
LD	5	13	0	0	58000000
LD	5	14	0	0	58000000
LD	5	15	0	0	58000000
LD	5	16	0	0	58000000
LD	5	17	0	0	58000000
LD	5	18	0	0	58000000
LD	5	19	0	0	58000000
LD	5	20	0	0	58000000
LD	5	21	0	0	58000000
LD	5	22	0	0	58000000
LD	5	23	0	0	58000000
LD	5	24	0	0	58000000
LD	5	25	0	0	58000000
LD	5	26	0	0	58000000
LD	5	27	0	0	58000000
LD	5	28	0	0	58000000
GN	-1
EK
EX	0	99	2	0	1	0		
FR	0	0	0	0	464	0
EN
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post #5 of 16 (permalink) Old 2008-10-05, 11:54 AM
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Quote:
Originally Posted by ericball
So copper tube or pipe is probably a good way to improve a Yagi-Uda or other antennas with straight elements, but not such a good idea for antennas with bends - use wire.
What about cutting the copper tubing at the proper angle and then soldering it together. I don't know how durable soldering a butted end together would be, but durability aside, do you think the performance would improve?
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post #6 of 16 (permalink) Old 2008-10-05, 12:03 PM
 
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Quote:
Originally Posted by 300ohm
That will be OK too. But if you have the pole going up the middle of the pipe, how are you going to keep it from rotating ?
I would either use a pipe clamp or something else to lock it in. Do you have any other ideas for me?
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post #7 of 16 (permalink) Old 2008-10-05, 05:31 PM
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Quote:
Do you have any other ideas for me?
Without seeing the exact situation, thats pretty hard, but here goes:

You could mount to a metal pole to the corner faschia board, and then u-bolt the antenna to it. Also, the u-bolt mount doesnt necessarily have to be in the middle, it could also be on either of the two sides.

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post #8 of 16 (permalink) Old 2008-10-06, 09:08 AM
 
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Quote:
Originally Posted by jschuk View Post
What about cutting the copper tubing at the proper angle and then soldering it together. I don't know how durable soldering a butted end together would be, but durability aside, do you think the performance would improve?
I just did a quick modeling test and 1/4"OD copper was 1% better than #10 steel, so the improvement isn't that great. (More tuning might improve that further, but probably not a lot.)

On the downside, in addition to the durability, the joints would be impedance transitions which would increase the internal reflections and probably decrease performance.
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post #9 of 16 (permalink) Old 2008-11-18, 01:25 AM
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Question Wave guide effect from tubing?

Wild guess, when using tubing versus solid conductors you are actually creating some wave guide which could confuse your antenna with much lower frequencies (microwave). Have you got the ability to measure if lower frequencies are also present? You could also try to fill your conduit with some similar to RTV??

Cheers!
RenÚ

Last edited by stampeder; 2008-11-18 at 10:50 AM. Reason: title added
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post #10 of 16 (permalink) Old 2008-11-18, 01:45 AM
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You could also try to fill your conduit with some similar to RTV??
Do you mean silicone sealant ?

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post #11 of 16 (permalink) Old 2008-11-18, 10:28 AM
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Yes, it would probably eliminate the wave guide effect. would also give greater capacitance separation I guess.
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post #12 of 16 (permalink) Old 2008-11-18, 12:45 PM
 
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Radio Frequencies travel on the skin of a conductor and the higher the frequency the less it wants to penetrate. Usually larger diameter conductors allow an antenna to have a larger bandwidth but the problem with making some antennas out of tubing is that tubing doesn't allow you to make sharp bends. Certain types of antennas need the sharp bends to operate as designed especially on uhf where the margin for error gets smaller.
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post #13 of 16 (permalink) Old 2008-11-18, 02:08 PM
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Quote:
tubing doesn't allow you to make sharp bends.
How about if only that portion was solid core? IE: fill the bent with solder or even solder twisted braid to the corners (must match the wave lenght)?

Cheers!
RenÚ
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post #14 of 16 (permalink) Old 2008-11-19, 12:43 PM
 
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Anything large diameter hollow or solid doesn't bend sharply without breaking. Not saying it can't be done but it takes special equipment and special material beyond most DIY. I don't know at what radius things would start to go bad on a G-H.
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post #15 of 16 (permalink) Old 2008-11-19, 02:39 PM
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Quote:
I don't know at what radius things would start to go bad on a G-H.
Modeling wise, its somewhere around 3/8ths of an inch. Around there, the 4nec2 program starts to kick out all sorts of warnings and errors, heh.

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