QUESTION: Chris, I am a new ham and want to erect a horizontal wire cut to 40 meters. I live in a retirement community with HOA and space restrictions. The only place I can place the wire is over the asphalt roof running from the back to the house front. I do have the option of over the aluminum carport roof.
I have read antenna books, asked this question on three other sites, spent hours searching the web have views but no replies.
I believe I need a counterpoise to reflect waves up into the atmosphere that would be absorbed by the asphalt roof.
Would one counterpoise be effective or would more be better? Should they be 1/4 wavelength or as long as the antenna?
This is my main question. Where to connect the counterpoise wires? I have a Palstar AT2KD tuner and good earth ground for the antenna and the am using and the station per NEC. No evidence of RFI and I can tune all bands I am using to 0 reflected power and 1:1 SWR.
As always the is more than one way to skin the cat, but I have read many conflicting statement as to where to connect. Should I connect to coax shield at the antenna feed point, to a good separate earth ground, I have read to connect to the antenna at the feed point.
ANSWER: Hey Steve - I'm assuming that when you say "a horizontal wire", you are talking about a dipole. With a dipole, you don't need a counterpoise. Dipoles are half wave antennas. A counterpoise is usually used with quarter wave, vertical antennas. The counterpoise electrically pretends to be the other half of a quarter wave antenna. A counterpoise does not "reflect waves up into the atmosphere", it helps the radiation pattern go sideways. 40 meters propagates mainly with ground waves so the signal will mostly hug the ground.
I would mount it on the asphalt roof. Absorption will be minimal to none since it's not electrically conductive. Some with HOA problems even mount dipoles in the attic space of wooden structures with asphalt shingles.
In Okinawa, I once had a dipole that was lying directly on a flat roof of a barracks with asphalt roofing and I managed to talk stateside on 15 meters without too much trouble.
WB6EEQ, Colfax, California
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QUESTION: Chris, Thanks for the reply. My plan is to erect one single end fed wire cut to 1/2 wavelength for 40 meters. It is good to know the wire can be laid on the roof or suspended a foot or so above the roof to be stealthy.
Since the antenna wire will only be about 20 feet AGL, eight feet above the roof, would a counterpoise be of any benefit? Increase DX Etc. There are people here who want all antennas banned so I want to minimize my time erecting the antenna. I would try a dipole but that is more wire, some type of center support all becoming more noticeable and adding fuel to the antenna war.
If I do decide to experiment, should the counterpoise be 1/4 wavelength or as long as the antenna?
Chris, I can not thank you enough for the information and your time and efforts helping others.
ANSWER: I think you're talking about an "end fed zepp" which I have never used. They must work without a counterpoise because they were first used on zeppelins, dangling in the air.
I've read articles that mentioned "counterpoise or a good ground". I have found that getting a very good earth ground can be very important in many situations. If I were you I would make that a priority. I've also heard that longer counterpoises have fewer problems.
Commercial broadcast antennas often use 90 to 120 counterpoise conductors. Not very stealthy.
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QUESTION: Chris, The antenna I an considering using is one single horizontal wire attached at
the "far" end with an insulator and rope to a tree and the feed end attached to the 9:1 unun which is attached to the mast. No dangling wires. I have spent much time and money planting copper, #4 solid copper, 5/8 inch soft copper tubing, everything tied together with #4 solid copper. As time and MONEY permits I will keep adding. One ground system for the antenna and one for equipment.
I have read that counterpoise has high voltage at the ends. Should I insulate the ends if laid on the roof?
The dangling reference was just to illustrate a point. Not suggesting that you dangle your antenna.
Congratulations on your grounding efforts.
Yeah, I understand that a counterpoise has higher voltage at the ends, but I don't think you need to worry about insulating if laid on the roof unless it is a conductive roof.