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Mounting A Mobile Antenna On A Mast

Discussion in 'Amateur Radio Antennas' started by BubbaDX, Jul 21, 2009.

  1. BubbaDX

    BubbaDX Member

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    Over the weekend I stumbled across a Yaesu 8900R and Comet UHV-4 antenna for sale locally on Craigslist. It was a good price so I bought it. The seller demonstrated it working and everything, but he had it mounted in his car. But I want to run this in my house as my commute to work is very short and I will get more use out of it in my house. I know its not the ideal antenna for mounting at home, but free is about as cheap as it gets.

    So here is my question: If I mount this antenna on a mast behind my house, do I need to isolate the antenna mount from the mast? Also, does any part of the antenna need to be grounded to work?



    Sorry if this question has already been answered. I have been googling since Sunday and have not found exactly what I am looking for. Thanks in advance for your help.
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  2. dudmuck

    dudmuck Active Member

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    You could call some ham radio stores and ask about a radial kit for the UHV-4.
    google found a post mentioning the radial kit, so it may be available.

    If not, then you may just want to leave that antenna for mobile use, and buy a different base antenna from diamond or whatever. That radio does 6m and 10m, but is of limited use there since its only FM.
    #2
  3. Quiksilver

    Quiksilver Active Member

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    #3
  4. Beetle

    Beetle Well-Known Member

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    You might experiment with four radials, each about 20" long, attached right at the feedpoint.
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  5. W5LZ

    W5LZ Crotchety Old Bastard

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    Can that antenna be used as a base/fixed antenna on a mast? Yes it can, if you make an addition or two to it. Very simply, you have to supply the part that the antenna expects to see when used on a vehicle, the other half of it, the counterpoise, groundplane.
    (I hate that word, 'groundplane', it's misused a lot. But in this case, it's exactly what's needed.)
    Like with most multiband antennas that require a groundplane, if you furnish a groundplane sized for the lowest band of use, the higher bands just use what they need and don't worry about the 'extra'. So, if you plan to use 10 meters, the lowest band for that 'Comet UHV-4', then that's the size of radial(s) I'd put under the antenna. Not gonna use 10, just down to 6 meters? Fine, do 6 meter radial(s) instead. Or just 2 meters isw that's all you want to use.
    So what size should these radials be? Good question, I can't answer that cuz I don't have one. They should be a minimum of the same length as the antenna, plus a little more probably. Lot's of 'skootch' room there, use whatever works for you.
    How well will it work? Can't say for sure, but it ought to work as well as if it were on a vehicle. Probably a bit better cuz it's higher (don't expect miracles ;)).
    That antenna has to be one of the best you could have! Why? Cuz it was 'free', naturally! I tend toward 'Comet' VHF/UHF antennas if I can, I've had good experience with them on mobiles. That certainly doesn't mean very much, I haven't tried them all, so take it for what it's worth. Also found one or two that were a PITA, mainly because they were a bit 'more' antenna than I thought they were (hit a tree limb, knocks down tree limb, that sort of thing, weird huh?).
    - 'Doc
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  6. BubbaDX

    BubbaDX Member

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    Thanks for the replies. What materials could I use for a 'ground plane'? I assume I need about 4 radials the full lenght of the antenna (52")?
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  7. W5LZ

    W5LZ Crotchety Old Bastard

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    Radials.
    You would need at least one. More doesn't hurt till it gets really ridiculous. What to make them out of? Well, as long as it will conduct electricity, whatever it is ought'a work just fine. No particular size, etc. Whatever you got that will 'do' it, sort of. Going to use guys on that mast? Use them. Or just wire strung up with twine? Or, weldin rods 'tacked' together to get the length? Coat hanger work too. You're only limited by your imagination (and neighbors sometimes?).
    It's something you have to experiment with, but longer is better than shorter.
    - 'Doc
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  8. BubbaDX

    BubbaDX Member

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    Thank you. That gives me a direction to go. I am going to put up a mast behind my house. I plan to get 20 feet of 1 1/4" galvanized steel pipe and bury about 4 to 5 feet of it in concrete. The first 6 feet above ground I plan to tie into my deck. The antenna on top of that should be about the height of my house. If not, I will add another piece of pipe (y). I figure as long as its not real visible from the street I won't catch too much grief from neighbors.
    #8
  9. Moleculo

    Moleculo Administrator Staff Member

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    The radiating part of the antenna needs to be isolated from the radials/groundplane part. That antenna has a PL-259 connection, so building this conversion is pretty simple. Go get an SO-239 barrel connector with the ring screws like this:
    [​IMG]


    It doesn't have to be that long, however.

    Get some type of angled metal bracket that is strong enough to support the antenna. Drill a 3/4" hole through the bracket to insert the barrel connector. Now just drill 4 small holes on each corner of the top part of the metal bracket and attach your radials some how. Now attach the whole thing to your mast. You're probably looking at under $10 worth of parts to do this.
    #9
  10. BubbaDX

    BubbaDX Member

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    Thanks for the replies. This does not seem like that hard of a project. I found some aluminum to use for radials. Does it matter if the radials are layed out in the shape of an X or is it OK to install them in the shape of a H? Will that effect the way it transmits?
    #10
  11. W5LZ

    W5LZ Crotchety Old Bastard

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    If that 'H' pattern of radials affects things at all it'll probably be the symmetricalness/symmerticity/whatever of the radiation pattern. Shouldn't think it's going to make a huge difference. Depending on just how far apart the legs of that 'H' are, you might could just use two instead of four. Try it and see.
    - 'Doc
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  12. Moleculo

    Moleculo Administrator Staff Member

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    I read somewhere a long time ago that you really only needed two radials for an effective groundplane, but people didn't like the way it looked, so manufacturers started adding two more to make it four. Is that an old wives tale or based on physics? I don't know. You would have to model it to see, I guess.
    #12
  13. mackmobile43

    mackmobile43 Jock Supporter

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    I would say 1 would work as well, just take a look at your basic dipole.

    Snake oil, I think not.
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  14. Beetle

    Beetle Well-Known Member

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    For a quarter-wave vertical, as you add radials you're reducing the IR loss (since you're putting them in parallel, the resistance decreases). Eventually you reach the point of diminishing return, and for local stuff and repeaters, four radials (in an X, not H) layout, are usually plenty.

    On HF, the more radials the better, generally.
    #14
  15. Marconi

    Marconi Supporting Member

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    Try this BubbaDX, and with 3 or more radials slanted down like the A99 GPK hub does, that is one on the pipe in the picture, you will have you a very good antenna. You will be surprised at how good if you get the bottom of the radials up at least above the highest point on your roof.[​IMG]

    This is a mobile L-bracket that goes on a mirror attached to a pole that will accomadate the hub form an A99. You could buy the GP kit and have four 72" radials that don't work as good as 102" whips, but they will get you a match in the high end of CB or you can add 3"-6" spacer and bring the resonance down into the middle of the band probably. The hub in the picture is homemade and has 3 holes for horizontal radials and 3 holes slanted down at 32 degrees for slanted down radials. Below is a picture of my Marconi 6 I call it.


    [​IMG]

    [​IMG]

    These are gate hanger mounts you can get at the Home Depot or Lowes in the fence department and they make very good and sturdy pole mounts.

    [​IMG]

    Here I am comparing signals at the same tip height with my I-10K vs. Marconi 6. The signal chart below has the milage for each buddy in the test. They did not know I was testing though, I only record RX signals and no DX working when I do this.

    [​IMG]

    Of course the topper as to why I have claimed for years now that most all of these CB vertical antennas perform just about the same, is because I'm located in an area with very good Earth's soil with very good conductivity. IMO this favors the 1/2 wave and then the 1/4 over the 5/8 wave---which really likes very poor soil to work over even extremently soil seems to help the 5/8 wave produce max gain in its lowest lobe, and not at the 35 degree angle it seems to produce over good or very good soil.
    Last edited: Jul 26, 2009
    #15


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