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Author Topic: HF Dipole Configuration question  (Read 3136 times)
N9XTF
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Posts: 227




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« on: February 25, 2013, 06:44:09 AM »

All, I apologize in advance as I'm sure this question has been asked and answered quite a few times.  I built an 80M dipole 10 years ago and used it on all HF bands 10M - 80M with great success using a tuner.  It was cut and resonant on the lower end of 80M.  I have been out of radioing for about 6 years and am getting all my gear back into action.  The antenna came down about 3 years ago as I had to cut down one of my 40' tall elms.  I no longer have a second tree close to support the second end and I do not want, for safety reasons, to erect it as a sloper having the end come near the ground.  I was wondering if it would be possible to affix the legs in the second story gutters on my house.  I have used insulated 14ga copper wire and I use coax center fed with 8 ferrite bead inside a PVC pipe stub capped with eyelets for wire connection and support.  Can I lay one leg on the front gutter and one leg in the back gutter.  The antenna would now be laying horizontal to the ground with the legs parallel to one another separated by about 35'. I would intend to put the coax connection at the peak of the roof and wire tie the antenna legs on the gutter supports.  This would resemble a three sided rectangle to provide a visual. 

I have read articles about loading gutters but it sounds like a poor idea.  If the antenna works in the fashion I have described, I am sure it will be a poorly operating antenna; I am trying to figure out a quick solution to getting an antenna up that I can work HF and make reliable contacts.  I cut a CB, Antron 99, antenna for 10M and use it quite well on 10M, 17M and 20M.  This antenna was installed 10+ years ago and shows no changes in operation.  I can load it on 40 and 80 however contacts are quite difficult to non-existent. 

In addition, I intend on using either my Al-811 or my L-4 for additional power on 40M and 80M.  I'm assuming the additional power will cause RFI problems around the house?

Again, please forgive me if this question has been asked and answered 100 other times.  Any other configuration ideas and or signal improvement would be much appreciated assuming I have the area to put it up without adding significant supports at this time.
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W5WSS
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Posts: 1747




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« Reply #1 on: February 25, 2013, 07:09:48 AM »

If I understand you correctly you are going to attach the gutters as an extension on the ends of the wires?

Pressing this doublet into multiband service.

If you must include the two gutters as antenna wire extensions

I would use a good high power 1:1 current balun up at the antenna feed point. Regardless.
This will help to balance the currents and voltages along the radiation path of the antenna.

Works to balance the system helps to keep the radiation along the antenna in it's normal condition for release.
The radiation wants to leave the wires equidistant relative to each other and wants to do so from the center outwards as frequency is lowered that distance moves farther outward along the wires.

Use caution when transmitting for safety that children can not contact the gutters.

Fatter material on the ends of a doublet will behave differently but will contribute to the total length of the two halves in a doublet.

If routing labor is not problematic then I would consider balanced line. a tuner and a 1:1 current balun with the proper connecting terminals for integrating the line to the antenna via the balun.

The tuner at the shack then balanced line to the 1:1 current balun up at the antenna
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K7KBN
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Posts: 2817




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« Reply #2 on: February 25, 2013, 07:12:19 AM »

If it's a full-sized 80 meter dipole it should be about 130 feet long.  If the ends are only about 35 feet apart, there will likely be such a great amount of phase cancellation that you'd be absolutely right: it will be a poorly operating antenna.

That said, however, you have a license that allows experimentation.  Try different configurations and find out what DOES work and what DOESN'T.
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73
Pat K7KBN
CWO4 USNR Ret.
N9XTF
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Posts: 227




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« Reply #3 on: February 25, 2013, 07:38:07 AM »

My intention is to just wire tie insulated wire on the inside of the gutter supports, I have no intention of connecting the antenna wire electrically to the gutters.  My intention in doing this was to have an antenna elevated off the ground.  One leg of the dipole would lay in the gutter, wire tied to the gutter supports just for support and the other leg in the opposite side of the house in the gutter in the same fashion.  The antenna would be three legs of a rectangle because the feed point would be at the peak of the house, then the antenna legs would go from there to the gutters and then make a 90 degree angle and follow the gutters.  I have no intention of creating a mechanical electrical connection to the gutter system; my intention is to just use them as a place to lay the dipole "legs".
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AA4PB
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Posts: 12907




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« Reply #4 on: February 25, 2013, 08:30:56 AM »

The close proximity of the wires to the metal gutters will couple the signal into the gutters. It will be almost like trying to load the gutters directly and it is not likely to work very well. That's especially true with the two legs of the dipole parallel to each other.
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N9XTF
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Posts: 227




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« Reply #5 on: February 25, 2013, 08:54:15 AM »

The responses are pretty much what I had expected.  Now the difficult part becomes trying to figure out how to configure a safe and useful antenna for HF service.  With a 35' tall house to the peak there should be some type of useful configuration that I can come up with, I will have to do some further research.
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W1JKA
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Posts: 1777




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« Reply #6 on: February 25, 2013, 09:57:27 AM »

 Any possibility of taking advantage of the 35 FT. peak at either end of house and making an inverted Vee,perhaps small trees,shrubs, fence, ect. on either side of house to connect ends to (above head level) ?
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W5WSS
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Posts: 1747




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« Reply #7 on: February 25, 2013, 12:39:19 PM »

OK, Yeah there are other options that may score better or not based on your operating goals.

Some ideas:

An inverted V could be a viable option
.
Do not exceed an inverted angle that brings the wire too close to each other.
Yes the insulated legs will couple to the guttering to a more or less extent whether one can tune the system and maintain the same field  strength relative to not installing the legs along the route through the guttering is a judgment call that really can only be answered with the use of field strength measures difficult to prove either way.
I make no assumptions either way.
 
For multiple band use.

Angle the wire to a safe out of reach distance above the ground and use an insulator and rope to tether the ends.
Use the 1:1 current balun ideally up at the doublet inverted V feed point and balanced line with a station desk top wide range tuner.
Hopefully you will enjoy an antenna that follows the expected reasonable pattern development.
And expected field strengths around that pattern.

Or instead build a G5RV with active balanced line relative to radiation.

 Omit the balun up at the feed point  refer to a graph that recommends a balanced line length that performs a impedance transformation and also radiates a E plane pattern. Locate the 1:1 current balun between the equipment and the antenna balanced feed line. and best but not as mandatory as a tune and balun capable of high power tolerance. 

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N9XTF
Member

Posts: 227




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« Reply #8 on: February 25, 2013, 01:25:44 PM »

I have both the 80M dipole and a G5RV on hand the only problem is trying to figure out the anchorage points that would be safe and not interfere with anything else.  As stated, I had them strung between two trees on my acre yard which worked out quite nice.  The house is too close to one of the original trees and the other remaining tall trees in the yard are too far away and inline with the house putting the antenna drooping on top of the roof.  I could use, but was trying to stay away from a ground mounted vertical.  I'll have to do some measuring, thinking and research to see if I can come up with something.  I was trying to do something at this juncture that was quick and economical.

Thanks for the input.
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W5WSS
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Posts: 1747




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« Reply #9 on: February 25, 2013, 03:31:07 PM »

OK That is wise  and most of all have fun at every phase of the build.
73
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K0ZN
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Posts: 1553




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« Reply #10 on: February 25, 2013, 07:31:27 PM »

If you have the wires very close to the gutters they WILL be coupled into the antenna and you have no idea of what is going on electrically in that situation; the
feedpoint impedance would probably be something "crazy" with a lot of reactance and likely loss in the system.
Short version:  bad idea. Do as much brainstorming as necessary to get the antenna wires away from gutters, power wires, etc.

73.  K0ZN
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W1JKA
Member

Posts: 1777




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« Reply #11 on: February 26, 2013, 06:58:49 AM »

  If you haven't already, you may want to check out [eham.net articles #20672] an inverted V 52 Ft. each leg from peak to or below eave level then back along each side of house.No trees needed.
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