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 XML Subscriber 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,

    Zach
     
  2. N1CZZ

    N1CZZ Ham Member 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 XML Subscriber 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?

    Zach
     
  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 XML Subscriber 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 XML Subscriber 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,

    Zach
     
  9. N1CZZ

    N1CZZ Ham Member 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 XML Subscriber 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?
     
  11. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    You can predict that, though, by making measurements. Ground losses make antenna bandwidths greater (wider) because they look like a resistance in series with the antenna. When they're minimized, you'll get SWR curves that replicate what SteppIR says they should be. Generally, you can also tell when an antenna is working well by getting comparative signal reports from distant stations who can compare your signal to those of others nearby to you. In fact, this is exactly what I do to figure out how well my own antennas work.


    You really don't have to do any of that. I'd cut a bunch of radials all the same length and connect them, and use it. 30 radials 33' long each will use up a 1000' spool of wire; so will 20 radials 50' long each, or 25 radials 40' long each. Pick whatever is most convenient to use, and connect them. When you have a lot of radials, their length is less critical than if you only have two, three or four. Basically, your metal roof would be an "untuned" ground plane system and if you could bond to it effectively it would work the same way as a bunch of wires cut to whatever length fits. I'd do the whole installation in one shot.
     
  12. N4ERZ

    N4ERZ XML Subscriber QRZ Page

    I understand what you are saying, but Steppir seems to disagree. They tell me that without using a MFJ(or similar) analyzer and working one by one with the radials, since they interact with each other, I will get substandard performance. I thought about a beam in lieu of the vertical, but several manufacturers have told me I need to clear the metal roof by 18-20' to prevent pattern distortion.

    I think that I am going to scrap the project for now. I just don't know enough about this to do it by myself.

    Thanks for the help, I guess I am destined to stick to my HT

    Zach
     
  13. WA8FOZ

    WA8FOZ Premium Subscriber QRZ Page

    Yes you do! This is not that hard, despite what some may suggest. Put the antenna up, ground it to the roof, make sure that the individual metal panels are well connected to eachother(multiple short ground straps screwed in with metal screws will be fine), and have at it! People have done this innumerable times, for decades, and it works fine!

    A large metal roof makes an excellent untuned ground plane ("image plane," really). I have no idea what SteppIr told you. Tuned radials are irrelevant outside of an elevated free-space installation. Mybe that's what they thought you were going to do.

    You can run the coax in by whatever route is most convenient. The SteppIr should tune up easily -and the internal tuner in your rig can touch things up, if necessary.

    It distresses when people make things harder or just more obscure than they need to be, especially for someone like you, an intelligent, careful guy who is starting out in this sublime hobby. This is supposed to be fun! Some of the fun is trying different things. It is good for morale to start out with something that has a high probability of success, which is what you are doing. So have fun!!
     
  14. N4ERZ

    N4ERZ XML Subscriber QRZ Page


    Thanks for the encouragement, I appreciate it. The folks at Steppir initially told me that the metal may, or may not function well as a ground plane. They told me to measure the resistance, but then added the caveat that even a positive measurement here would not verify that it would function as intended. I then replied to them about abandoning the idea of using the roof and using their radial kits along the metal roof instead. They replied that with each radial in contact with the metal roof, each one would "require very different lengths and that would have to be arrived at through actually using something like an MFJ-259 to determine the resonant frequency of each radial pair".

    I don't have a MFJ259 and with the price of the Steppir I am stretching the budget as we go. I just cannot justify another (essentially one-time....for now) purchase of something I don't know how to use.

    It certainly seems like this project is growing and growing in time, money and difficulty. There is nothing I would like more than to be on HF. When I was originally licensed as a teen in the early 90's I couldn't afford the gear and let everything expire while in college and starting a family. I just got re licensed with the goal of HF work specifically aiming for the April rookie roundup, but that won't happen. I do feel like I have rushed into this a bit and perhaps it is best to step back and reevaluate what I can truly do.

    Thanks for the help, I am a a bit technically challenged at the moment....I'm also going to go to the next club meeting a beg a bit more, although it seems "roof" and "volunteer" don't mesh well.
     
  15. K9MRD

    K9MRD Premium Subscriber QRZ Page

    <<They replied that with each radial in contact with the metal roof, each one would "require very different lengths and that would have to be arrived at through actually using something like an MFJ-259 to determine the resonant frequency of each radial pair".>>

    I agree with WA8FOZ. When many radials are used with an elevated vertical, they Do NOT have to be tuned. This is what you have with the metal roof, i.e. an image plane. I would hope there is a communications problem rather than technical understanding regarding the manufacturer's input. How well the roof works will depend on how well the sheets are bonded, overall size of the roof, and the frequency used.

    Don't give up! Give it a try....I think it will work well.
     
  16. N4ERZ

    N4ERZ XML Subscriber QRZ Page

    Many we are having a communication issue - although I have written much the same things as I have posted. When mounting the antenna, it appears that it mounts on a standard mast/pipe/etc... I can put that at any height above the roof that I want (within reason). Not sure that it matters, but the roof is rather flat, approximately a 2/12 pitch. Originally, for ease of installation, I would prefer to have it low to the roof and have the radials running along the metal of the roof. It would be a bit more challenging to have the antenna a few feet off the roof and the radials sloping. I'm not sure that I am interpreting your post correctly, which way would you suggest?

    Also, as far as bonding to the metal roof, what is the preferred way? The metal on the better of the two buildings is a painted and corrugated (galv. steel base - MAYBE) roof that is merely lapped over the next sheet with prefabricated trim pcs. installed around the perimeter. Not sure how great that would be. Also, with the roof being so flat, it would be better for me not to mount it at the ridge, but in the middle of one side so I could gain some distance between the antenna and a neighbors house...I do fear interference a bit.

    Maybe we can get this worked out....I am moving towards cautiously optimistic....maybe :)
     
  17. WB2WIK

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    Low to the roof. You can lay radial wires directly on the roof. Their length is absolutely, positively not critical when you use a lot of radials -- I couldn't care less what SteppIR says, it's nonsense if they say radial lengths over a metal roof are critical.

    I'd put the vertical in the middle of the roof (dead center) if possible, to allow the best ground plane around it in all directions. I'd bond the vertical base to the roofing using multiple (say four) heavy gauge wires, #6 AWG or so, that are as short as possible attached to the roof using large sheet metal screws: Hardware stackup would be screw head-flat washer-heavy wire-flat washer-star washer-roof. This would sandwich the wire between two flat washers. If the roof is painted, scrape the paint away right at the screw hole. Once screwed in, caulk over with roofing cement (just a dab, doesn't take much) to weather seal it. Run the four wires in four different directions (90 degrees apart) to spread the attachment over the largest possible area and keep the current in each connection point 1/4th of what it would be with just one attachment.

    Frankly, I'd supplement that with copper radial wires, anyway -- probably at least 20 of them. They don't have to be any specific length but since wire comes on 1000' spools, if I used 20 radials, they'd each be 50' long. Or 25 that are 40' long. I doubt it matters in the slightest, in this situation -- and I've done "metal roof installations" for verticals many times.

    This is not a big job.
     
  18. N1CZZ

    N1CZZ Ham Member QRZ Page

    Like WB2WIK said for the most part,
    and I stated in post two it will work very well, but a few more thoughts.
    I think it is very important to keep the vertical mounted as close to the roof as possible in order for the roof to help and act like you want.
    Trying to tune radials laying on the metal roof would probably be a mute point.
    As far as laying some down like WB2WIK says, it can't hurt, but I don't think I'd put forth the time and money, but that's what makes us all different.
    All this being said, I would hate for you to spend the money based on something I said and not be happy, but I often think that it would be neat if the next place I buy in the country had a big metal building the first thing I would do is put a vertical on top, one like the steppir, or one using an auto tuner.
    If we were to divide the antennas out there used by all hams into two categories based on performance, the upper half and lower half. This set up in my opinion would be in the upper half as far as performance, not the lower.
     
  19. N4ERZ

    N4ERZ XML Subscriber QRZ Page

    I will most likely install the radials as well to insure that I have done everything in my power to be "correct" and efficient. Also - I think that I will use their pre-packaged radials (16' for the BigIr) since it is a bit easier and less soldering on my part. I know it is a bit wasteful for money, which is somewhat tight, but it will take a little "pressure" off. A few more questions -

    Should I be worried at all about interference with 2 houses that are approx. 40' away from the building and of a similar height? Is there anything I can do to minimize the risk? One neighbor is a bit less than friendly, so I would prefer to minimize any impact. I am only here during the day (I hope to operate remote at night with a Kenwood TS480)and actually think there would be retribution in the way of damage, which is a petty game I would rather not play. Also - I would be using maximum 200 watts from the TS480.

    There is an optional balun - should that be purchased?

    With the 16' radials, is it really just connect as many as possible and lay them out somewhat evenly across the roof?

    Finally - the Steppir is 5-6 weeks backordered. Is that the best option? I don't mind waiting if it is...
     
  20. WB2WIK

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    No way to guarantee anything, but I doubt you'd have any problems. If we need guarantees in life, none of us would ever do anything.

    I wouldn't bother with it. And it should be a unun, not a balun: Coax is unbalanced, and so is the vertical.

    I'm not familiar with the "radial kit." Are you talking a SteppIR small vertical (20 through 6m) or the BigIR that also covers 30-40m and has an optional loading coil for 80m? Big difference in the radials required.

    The SteppIR verticals are good but of course complex (have moving parts and require a control cable and line, and a control box to operate them). For remote ops, I think you can do that once the control box is pre-set, using a computer interface (although I've never done this). The smaller vertical doesn't require any guying, but the bigger one (BigIR) does -- for sure. That involves lightweight rope guys tied about midway up the vertical, and a place to anchor them on the roof. The BigIR without any rope guys does not survive windstorms well. Don't ask how I know that.:p
     
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