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Tower Install

Discussion in 'CB Antennas' started by edfiero, Oct 22, 2018.

  1. edfiero

    edfiero Member

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    I'm going to be putting up a 30ft Rohn tower. Antenna will be a 3 element.

    I'm going to attach it about 20 / 25ft up to the gable of the house.



    Question, how much of a concrete base do I need to put this thing in? I see people quoting a cubic yard of concrete, but that seems to be for free standing towers, not one that will be attached to the house.
     

  2. Blackcat630

    Blackcat630 Sr. Member

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    For something like that I would think 3x3 would be sufficient. Check the frost line for your area and make sure your depth is below that... my .02
     
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  3. Road Squawker

    Road Squawker Sr. Member

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    err.......... 3x3(x3) is a yard
     
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  4. Mudfoot

    Mudfoot Sr. Member

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    Cubic yard will make you sleep at night, plus allow for a little more height, sometime.
     
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  5. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Nope, 3X3X3 is a cubic yard. they are talking about 3'x3' + 3 inches below frost line.
     
  6. Blackcat630

    Blackcat630 Sr. Member

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    That's kinda what I was thinking. Room to grow a section or 2... If your going to go through the trouble of using rohn & a decent concrete base along with attaching to the house I would probably go 40-50 ft. Wind load of a 3 element 11 meter beam & rotor shouldn't stress things too much... as long as you don't go sticking 20 ft of mast pipe out the top of the tower. I would set the rotor as low as possible in the tower and set the beam just above the nose cone. You could even put a few feet out the top and put a omni above the beam... again my .02
     
  7. Road Squawker

    Road Squawker Sr. Member

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    I don't think the OP even mentioned the frost line;)
     
  8. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    Every concrete construction need to be below the frost line. Here in Louisville that would be 24" below the surface.
     
  9. edfiero

    edfiero Member

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    you guys are putting a damper on my plan to put 2 bags of sackcrete in a small hole and call it a day. Isn't the house mount going to take 90% of the wind force, and very little be transferred to the ground?
     
  10. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    For such a small tower that is bracketed to the house you do not need anywhere near a cubic yard of concrete. I had a 48 foot tower temporarily mounted to a building at the eve so about 20 feet up and the bottom was actually on the ground. I bolted a piece of 3/4 inch plywood to the bottom and drove three pieces of pipe thru holes in it to pin the bottom and keep it from moving. This held a VHF colinear groundplane and two VHF commercial yagis and was up from the fall thru the winter until mid-summer the following year and never moved. Stability was critical as the yagis were receiving/transmitting program material for a commercial broadcast installlation. When I moved into my new home I built 27 years ago I put up 24 feet of what was normally freestanding tower (the same type used in my previous example at the radio station) and installee one set of guys and also mounted it on plywood pinned at the bottom to keep it from moving. This was NOT mounted to a building. It supported a Cushcraft A3 HF tribanded and an 11 element 2m yagi from fall thru winter until the following summer when I was able to dig a hole and plant the tower properly. I have yet to see a bracketed tower need to have the base cemented in below the frost level to be honest as long as the soil is compact and not just loose backfill and tryst me......we have frost up here. I HIGHLY recommend any attachment done to the eves however be done using reinforced mounting points and do NOT rely on just the finish boards to support it. A 2x4 across the eve well anchored with lag screws should be used with the tower mounted to the 2x4.
     
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  11. Tallman

    Tallman W9WDX Amateur Radio Member, KW4YJ EXTRA class

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    If you want to use concrete a hole about the size of a five gallon bucket would work out fine.
     
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  12. Redbeard U812

    Redbeard U812 Active Member

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    I drove a 2" dia. pipe with a fence post driver (Home built variety). Sunk that puppy 6'~8' deep, a piece of 1.5" dia. pipe fits into the top of the driven 2", only about a foot is needed to create a nipple which to slide another 2" over to extend upward. Was doing pretty good until the rains came. This "was" freestanding, my total height is 38'. but not all 2". Well rains came, with that wind.......noticed a lot of wiggle. Found it was wallerin out and sinking. We have black gumbo, which sticks worse than dog chit, slick too. had to install (4) 2" dia. laterals at 90 deg. about 3' length right at the base, good thing I weld. Stopped the sinking but not the wallerin due to wind. Dug out around vert. in ground about 1' out and 2' down, dumped concrete. Now the whole plug wiggles.....damn. Added guy wires.

    Guess what I am getting at is consider the elements. Plan for the worst. Be ready to improvise your plan, because you will. I suggest some concrete. Or like Capt. Kilowatt did by spreading or displacing the load across a wider area. Sure don't want to find tower laying across the deck, neighbors drive, or your own roof.
     
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  13. loosecannon

    loosecannon Sr. Member

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    edfiero,

    what you are looking for here is a consensus of opinion regarding whether or not what you are planning will be safe.

    That is not a good idea and here is why.
    none of us have to live in your house, or deal with the repercussions of any mistakes in our judgement.
    only you will have to shell out the money, or apologize to a neighbor or whatever else if that antenna comes down.

    will the eave mount eventually waller out the holes it lives in?
    will the concrete base eventually sink?
    will it tear your wall down in a strong wind?

    these are the concerns you should have, and these concerns should be the reasons for doing this the right way. what is the right way?

    it's the way that has been established by engineers who stake their careers on being right about these things. It's the way that has been rigorously tested by numerous industries. it's the way that people are willing to warranty.

    none of us fit these criteria, and even if some of us might be engineers, we wouldn't put our stamp on anything unless we'd done a site survey, drawn up the plans, and had them checked.

    so, the real question becomes, "how will you sleep at night when the wind is howling outside your window?"

    will you take comfort in our advice and drift off to a restful slumber? or will you freak at every creak?

    we don't build for what we know will happen, we build for what might happen.

    this was meant to be helpful, i hope it was.
    LC
     
  14. kopcicle

    kopcicle Sr. Member

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    I always dig a hole big enough for a dead body , just in case.
     
  15. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    If he bolts it to the house as he suggested it won't move. Your problem was because you tried to make it freestanding. My first installation was a piece of 3 inch black iron pipe in the ground about 18 inches with a very small amount of concrete. The soil was heavy red clay. That pipe was bolted to the house eve. Another piece of 2 inch black iron pipe was sleeved inside collars welded to the 3 inch. This allowed me to raise and lower the antenna. I had a Wilson Shooting Star about 32 feet to the boom and I was wide open to the winds for about 270 compass degrees. It lasted for years until I got a tower. Anything very long WILL move in the wind and eventually loosen in the soil unless you provide a second anchor point near the top.
     
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