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Thread: Roof mount or Chimney mount yagi?

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  1. #1
    Join Date
    Apr 2003
    Location
    Maryland
    Posts
    3,452

    Default

    I am thinking (at least to myself) about getting a small mini-beam and putting it on my roof. Now I know a mini-beam will give me mini-performance, but a) I would like to keep a relatively low profile (just moved into this neighborhood) and b) am interested in learning about beam headings/propagation & long/shortpath openings.

    If I got a small mini-beam, like a Cushcraft MA5B (7 foot boom, 17 foot elements), should I put it on my roof using a tripod (like a Glen Martin) or mount the mast to my chimney. The chimney would be easier (and cheaper), but I don't want to destroy my chimney. THAT would be a problem.

    Anyone with experience/advice with roof mounting yagis? A tower is out for now.

    paul

  2. #2

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    Of what is the chimney made? If it's brick, then I wouldn't think there would be any problem. I would, however, think that mounting a tripod on the roof would introduce the possibility of roof leaks.

    73
    Richard
    KI$DOK

  3. #3

    Default

    Of what is the chimney made? If it's brick, then I wouldn't think there would be any problem. I would, however, think that mounting a tripod on the roof would introduce the possibility of roof leaks.

    73
    Richard
    KI4DOK

  4. #4

    Default

    If your chimney is made like mine, it is going to be here a long time after the entire neighborhood is destroyed by an asteroid collision!

    However, if your chimney is used (for a fireplace, water heater, furnace, etc.), then the smoke and fumes are going to greatly hasten the demise of your antenna! Aluminum doesn't like the products of combustion very much. However, the products of combustion definitely like aluminum! That is, they like to "eat" it!

    As such, it is my opinion that a chimney mount should not be used for any long term installation.

    Glen, K9STH

  5. #5
    Join Date
    Apr 2003
    Location
    Maryland
    Posts
    3,452

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    Brick chimney, we do not burn wood in the fireplace, however we do have a furnace! While I am SOMEWHAT interested in the lifetime of the antenna (a couple hundred bucks), I am far more concerned about the lifetime of the chimney (a couple thousand bucks). I read WIK's comments against chimney mounts once, mentioning if you want a pile of bricks instead of a chimney go for it!

    paul




  6. #6
    Join Date
    Jul 2001
    Posts
    21,474

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    I've mounted several tripods on several roofs, and never had a leak as a result. However, I would NOT put anthing up on a chimney larger than a good sized long-distance TV antenna or multi-element 2 meter beam !

    My biggest roof installation was a 15 foot self supporting tripod that held a "GemQuad" boomless, full-sized 10-15-20 meter cubical quad antenna. I ran threaded rod through the roof and a set of 2X4s that spanned a couple of the rafters. That setup was so strong that the roof would have been torn away before anything came loose!

    The house was 2 stories plus an attic, and the center of the antenna was 15 feet above all that. I regularly worked phone patches into South America with outstanding results using that setup!

    73 from Jim AG3Y

  7. #7
    Join Date
    Jul 2003
    Posts
    1,329

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    As a person that formerly serviced HVAC including gas/propane, oil, and heat pumps, I HAVE seen a couple of chimneys.

    There have been QUITE A FEW that I wouldn't mount ANYTHING on. I've seen old brick chimneys that you could almost tip the exposed portion over and dump it down the roof.

    I would be darn careful, here. I don't know what ice/snow/winds you have in your area, how big/old/strong your roof or chimney is.

  8. #8

    Default

    </span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (K3STX @ June 23 2004,09:55)</td></tr><tr><td id="QUOTE">I am thinking (at least to myself) about getting a small mini-beam and putting it on my roof. Now I know a mini-beam will give me mini-performance, but a) I would like to keep a relatively low profile (just moved into this neighborhood) and b) am interested in learning about beam headings/propagation &amp; long/shortpath openings.

    If I got a small mini-beam, like a Cushcraft MA5B (7 foot boom, 17 foot elements), should I put it on my roof using a tripod (like a Glen Martin) or mount the mast to my chimney. The chimney would be easier (and cheaper), but I don&#39;t want to destroy my chimney. THAT would be a problem.

    Anyone with experience/advice with roof mounting yagis? A tower is out for now.

    paul[/QUOTE]<span id='postcolor'>
    I did exactly what you describe here with a Mini-Quad. During a wind storm it came down. It sheared off at the mortar about one foot from the top.

    The mortar just won&#39;t take much shear force caused by wind pushing the antenna.
    F=ma

  9. #9

    Thumbs up

    Paul, I have used ten and fifteen foot tall tripods at three
    different QTH&#39;s for mounting a Mosely TA-33, rotor, and
    two meter beams (stacked 11&#39;s) with a Ringo Ranger on top.
    Unfortunately the tripod manufacturers I had used are not in business any longer. I will say that I never had a bit of problem with roof leaks or structure damage. The fifteen foot tripod required some carpentry to get all three legs onto a roof joist, but that only involved using some 2 X 4 and
    a few 16p nails. The Glen Martin roof towers are built a lot
    stronger than the Tripods I used and should be more than
    sufficient for your use. Stay away from chimney mounts as
    smoke and heat are corrosive over time.
    73, Cal K4JSR

  10. #10

    Default

    Hi Paul&#33;

    Just a few comments concerning your antenna mounting situation.

    First off, none of us can tell you if your chimmney is sound. #I suggest you have it inspected by a licensed contractor if you are serious about that type installation.

    I can tell you from my own experience that mounting it on the chimmney is NOT the best thing to do. #While living in Norway, I had mounted a HQ-1 Mini-Quad #that way. #While it made it thru the winter, I had to replace vituually everything that held it together, due to corrosion and heat from the chimmney. Yes, I burned a lot of wood, but even without that, anything you burn and send up the spout will have an effect on the antenna. #It spent the next two years on a deck mounted tri-pod (hi).

    I would suggest that you give consideration to a good, ground mounted vertical antenna rather that the smaller beam. #You can mount it in an out-of-the-way location, which will conceal it from view. #AND, you do not have the added expense of a rotor system, and the extra control cable.

    The beam you mention will set you back as much as a good vertical, and give you less band coverage. #And a set of 17&#39; elements, to me at least, are really not that stealthy on your rooftop&#33;

    You might also consider a Delta Loop, fed with open wire line, for multi-band coverage. #They work well, are relative inexpensive, and can also be installed &quot;out of sight&quot; in most locations.

    Whatever way you go, good luck&#33; #

    73, Jim/k7unz

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