vertical - metal roof in lieu of radials?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N4ERZ, Mar 21, 2011.

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  1. N4ERZ

    N4ERZ Ham Member QRZ Page

    I am considering a vertical antenna (steppir perhaps) for my office. It's only 1 mile from my house and I could have an HF setup there as opposed to my house which has many obstacles (small yard, neighbors, my wife...). On Steppir's website they make a reference to a metal roof being a good ground replacement for radials and a great counterpoise. I'm wondering if anyone has done this before? My warehouse has an old, somewhat rusty galvanized standing seam roof and my office has a corrugated metal roof. I could use either building, but the office makes more sense since it has internet and I can envision remote access etc...

    Is this realistic or just advertising? Any reliable way to know if this was going to work?

    Thoughts are appreciated,

  2. N1CZZ

    N1CZZ XML Subscriber QRZ Page

    My thoughts, but I am not a guru. Raised verticals require tuned radials and grounded mounted like alot of the area around it to be conductive. The large conticous metal roof and the fact that it is connected to earth below, or you would make sure it is bonded well to the earth, would make it more like a ground mounted vertical on a bump or small hill. I think it will work very well for you.
  3. N4ERZ

    N4ERZ Ham Member QRZ Page

    Thanks for the reply. I emailed Steppir to ask their opinion and got this as part of the reply to test and see if it would be truly functional. ...."take an Ohm meter and check the resistance between panels.
    It should be very near "0" Ohms. However, even with a low DC resistance it does not
    assure a good RF connection"

    The part that bothers me is there is no assurance, even after testing, that it will work. As a rookie, I am not certain that I will know if it is functioning at 100% or not. I hate to proceed into uncertainty...

    Any other thoughts?

  4. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    If it's an industrial building with a metal roof anyway, I don't see the big deal:

    Try the metal roof as a ground plane (be sure to electrically bond to it, very well, using multiple low-inductance paths); if that doesn't work well, add copper wires as radials, laying on the metal roof. They can be secured using roofing cement, or just tied off at the corners of the roof or whatever is convenient. One way or the other, you'll have an antenna that works fine.
  5. N4ERZ

    N4ERZ Ham Member QRZ Page

    It is an industrial building and it appears that the radial kits are pretty cheap, so I might go for it. With that said, I would prefer to bring the coax and control cable through the roof (vent pipe style) and straight down into an office... I'm assuming this is less than ideal for grounding, but am not 100%. Any thoughts on that?
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Kits are fine, but all you need for radials is "wire," preferably pure copper wire. And some end ensulators, and crimp or solder lugs to attach to the base of the antenna. I can make twenty 50' long radials from one $40 (1000' long) spool of wire, twenty lugs and 20 small insulators, and maybe a ball of string. Might cost $60 total for everything, and take an hour or so.

    That should work fine. You'll never achieve an earth-connected RF ground on a roof. You should always add a lightning discharge ground, securely connected to the base of the vertical (or its support pipe) and taking the shortest possible outside path to earth. Bringing in cables close to ground level provides a way to ground them near earth just before they enter the building, which is very nice, but you do what you have to do.
  7. 4L4AGU

    4L4AGU Ham Member QRZ Page

    It's an interesting question for me also. Our rural house is made of wood, but it's roof is made from pure aluminum pieces, riveted to each other, so roof panels have good contact with each other, and roof has no contact with ground - measured DC resistance is greater than 2 megahoms. Total roof area is 13x13 meters. It should make not so bad radial system for 40 meter quarter wave vertical, right?
  8. N4ERZ

    N4ERZ Ham Member QRZ Page

    My concern is that A. I won't know if the roof is performing as well as possible and B. if the roof ground fails to work, I am not thrilled about having to measure and cut each radial over and over for tuning purposes. That is a lot of trips from the roof to the office and back....especially for someone that has never done this before...

    Thanks for the thoughts,

  9. N1CZZ

    N1CZZ XML Subscriber QRZ Page

    Answer to your A. Will anyone really ever know if any antenna system is working as well as possible? If that is going to be an issue, one should hang it up. In fact, that falls in line with a perfectionist whose life is constantly hindered by some unrealistic self imposed ideal. In other words, I don't find A to be of much value, determine how you think it will work, but if you apply the "is performing as well as possible" to any antenna system you won't put any of them up.
    B It probably will work real well, but if it didn't, the fix would not be tuned radials sitting on or above the metal roof.
  10. N4ERZ

    N4ERZ Ham Member QRZ Page

    While I agree with you about not achieving true perfection, I do think there is a vast difference between 30% efficiency and 90%. I would like to know approximately where the performance would be to make decisions to consider other options.

    If the fix isn't tuned radials, what would it be?
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