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Author Topic: Supporting dipole ends....water pipe?  (Read 4355 times)
W0XXX
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Posts: 25




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« on: October 27, 2011, 06:36:26 PM »

Here in the Chicago area, we are plagued by small residential lots. I have a vertical up now, and I'd like to put up a wire as well. About the only way I can do it, is to hang it between two water pipes attached to a wooden fence. I was thinking of attaching two ten foot sections, that gets it 20 feet high.

Has anyone tried this, and does it make sense?
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N3WAK
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« Reply #1 on: October 27, 2011, 07:00:10 PM »

I guess a lot depends on what the water pipe is made of, how thick it is and how the two halves are connected--welded, telescoped?  Also, whether you're going to guy them. 

I have built a couple of PVC masts about 18' high, with 2" and 1.5" PVC schedule 40 pipe telescoped together and fastened with a couple of 1/4" stainless steel bolts.  Light duty, but works great.  I have also used thicker OD PVC, and it's more rigid. 

You can also use galvanized fence poles (Lowe's, Home Depot), pipe from a plumbing supply house, or guy some Radio Shack aluminum TV masts, which come in 10' and 5' lengths that fit together. 

There are a lot of possibilities.  You might even want to anchor one end of the antenna (or the guy) to the highest part of your roof.  Or, if you have a chimney, mount a chimney mount TV mast on it and use it as the center support for an inverted vee. 

I am a real fan of inverted vees rather than flat-top dipoles.  Yes, I know as a general rule that flat-tops are "better," but inverted vees only require one support and the coax doesn't weigh down the middle of the antenna. 

Good luck.  73, Tony N3WAK
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W0XXX
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« Reply #2 on: October 27, 2011, 07:37:21 PM »

I'm not opposed to doing an inverted V, and a pvc center support might work out pretty well, and be easier. I would imagine the center support should be at least 20 feet tall huh?
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N3WAK
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« Reply #3 on: October 28, 2011, 06:03:49 AM »

Tom:  An antenna's ideal height depends on so many things.  At 80 meters especially, an inverted vee on an 18' mast is going to be an NVIS antenna--not good for DX but great for contacts out to about (I think) 600-800 miles.  At 10 meters, 18' is slightly more than a half wave, great for DX.  (However, the effective height of an inverted vee is usually about 2/3ds of the central support's height.)  For 10 meters, that will be a fine DX antenna. 

A light PVC mast as I described is going to be about 18.5' high, if you telescope the tubing 18".  Put an eyebolt at the top to hang a 1:1 balun, if you use one.  This will work great.  As I said, you can use heavier tubing, so long as it telescopes--you can find OD and ID dimensions of schedule 40 PVC easily on the web.  Or, you could telescope three sections together, but the higher the mast the floppier it becomes.  You could also use fiberglass tubing, from DX Engineering, MFJ, and others--I think HRO sells the MFJ mast, for instance.  I bought the 50' DXE mast kit, but only use the bottom sections for rigidity, and the antenna wires act as guy wires.  (Make sure the inside angle of the wires is at least 90 degrees.)  You can also telescope a 2" + 1.5" + 2" together (or something like that arrangement) with a substantial overlap on each side, to get a bit more rigidity and height.  But my experience with PVC is 25' is about the max you can get, but it needs to well "guyed" with antenna wires.  I have had better success with masts 20' and lower.

A quick and dirty PVC 18.5' mast is going to cost about $20, if I recall; the stainless hardware cost me more than the actual tubing.  Or, you can use gray, UV-resistant schedule 40 tubing from the electrical section at Lowes (versus the white, non-UV-resistant stuff from the plumbing department at Lowes).  If you make a fan dipole, and can feed the legs out from each other (perpendicular would be ideal, like a maypole), you can cover several bands depending on space limitations. 

I know a lot of hams will insist on a 50' tower and a triband yagi.  That's not feasible for me, or, I suspect, for many hams.  A wire antenna on a relatively short central support might not win you all the big DX contests, but it is sure a cheap, effective, and fun antenna for many of us.  The PVC mast is so portable and cheap that you can take it down, easily move it, and alter it on your next free weekend if you want to experiment with a different arrangement. 

I encourage you to experiment with wire antennas.  I have built a bunch of them, fed with coax.  However, here's another option: http://www.qsl.net/wb1gfh/antenna.html

73, and good luck!  Tony N3WAK
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W0XXX
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« Reply #4 on: October 28, 2011, 07:42:34 AM »

Thinking out loud here....wouldnt a multi band vertical and an inverted V have the same polarization?
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N2EY
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« Reply #5 on: October 28, 2011, 10:40:40 AM »

wouldnt a multi band vertical and an inverted V have the same polarization?


No. Why would they?

73 de Jim, N2EY
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K2OWK
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« Reply #6 on: October 28, 2011, 02:32:34 PM »

An inverted "V" is both horizontal and vertically polarized an advantage for talking to either polarisation. It is a disadvantage for noise as it picks up noise in both polarisations.

73s

K2OWK
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WB6BYU
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Posts: 13486




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« Reply #7 on: October 28, 2011, 03:00:54 PM »

The vertical polarization of an inverted vee is relatively insignificant.  You may get
measurable amounts off the ends if the angle between the wires is rather sharp, but
even then it's at least 10dB down from the horizontal polarization - you can easily
get more vertical radiation from the coax if you don't use a good balun.

I'm not sure where the myth of the mixed polarization of an inverted vee came from,
but it is time to put it to rest.
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W0XXX
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Posts: 25




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« Reply #8 on: November 02, 2011, 05:34:25 PM »

Here's what I did...

I had an Alpha Delta EE in the garage attic, and she wasnt happy. I moved it out side and supported the center on 20 feet of PVC pipe. I figured the antenna might react to the metal water pipe, to I went with PVC and a couple of rope guy lines. It works ok...just ok. I compare it to a 4BTV, which has a really good radial system attached to it. As expected, some stations are louder on the V then the vertical. The EE has its ends pointed East and West, but its a bit close to the house....small lots here in Chicago. The EE is 80 kHz wide to 2:1 on 40m.

One thing is obvious, the EE is electrically quieter then the 4TBV which I really like. Now the search goes on for a higher non-evasive installation...
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K2LGO
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« Reply #9 on: November 02, 2011, 05:48:31 PM »

To W0XXX..
   I have my inverted v mounted just as you propose, with sections of TV mast clamped to the corner posts of my fence...Posts are six feet high, and I have about another 7-8 feet of TV mast above that held to the fence post with two big radiator type hose clamp (available at auto and truck parts stores)...
Been working great for years...Probably one ten foot section of the mast on each fence post would be about all I would go for height...that would be three feet on the post to hold it, and 7 feet sticking up to attach the antenna
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W0XXX
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Posts: 25




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« Reply #10 on: November 05, 2011, 06:33:23 PM »

Moved it today....

Mounted it on 30 feet of Radio Shack antenna mast (3 ten foot sections). Dont see much of an improvement, but Ive only had it up since this morning.
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KC0KEK
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Posts: 144




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« Reply #11 on: November 20, 2011, 05:25:54 PM »

I just put up an OCF dipole. Fortunately there's a tree in exactly the right spot for the short leg. No such luck for the long leg. Right now, it's tied off to the neighbor's fence, but I don't want to risk the wind causing the wire to tug so hard that it damages the fence post. So I'm going to see if I can find a purple martin birdhouse kit. I don't know anything about birds, but every purple martin birdhouse I've seen appears to be atop at least a 20 foot pole. If it works, it beats having just a piece of pipe sticking out of the ground.
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