Monday, February 8, 2016

My Other Project

I've spoken several times about my project to convert my G0704 mill to CNC, but this winter I have a project that has taken precedence.  I need to do some serious maintenance on my ham radio tower installation.  As in rebuild a lot of it.  It was put in place around 1990. 

I have just about the smallest tower that hams routinely use: 20' tall.  With a mast in it, it gets the top antenna up to 28'.    Most guys use a couple of 10' sections of Rohn steel tower (25G), burying one section a couple of feet and using one or two other sections.  When I put it in I designed a method of leaning the tower over to work on or remove antennas.  Living in hurricane country, I wanted to be able to get the antennas off easily.  My friend N4RFC (in the blog list) used to live a couple of blocks away, when we both lived in South Florida.  When Hurricane David was approaching, he and I took down both his antennas and mine, but then had to help another guy in the neighborhood take down his antennas.  He had broken his leg and was on crutches, so he was unable to do anything to help take down his antennas.  By the time we got to his place, the winds were getting up 25 or 30 mph and the two of us were on this third guy's roof, on a ladder, taking down his antennas.  That was my motivation to never have to do that again.

Mine is an aluminum tower, so it's lightweight, and the tower has a hinge built onto its base in the form of two "ears" of angle aluminum put in place before the cross piece was welded on.  I poured a concrete base and sunk a couple of redheads that those hinge pieces bolt to.  It's fairly easy to walk the tower up with just that hinge, but I wanted a way to crank it over.  A friend had a 10' long piece of 2 1/2" schedule 40 steel pipe that became my method.  I dug a hole 3' deep for it and put it in the ground at the same time I was pouring the concrete pad.  The concrete doesn't encapsulate the entire 3' of pipe in the ground, but just the top foot; the rest is just in compacted soil.  Once the pipe was up, I mounted a boat trailer winch to it at waist height and hung a pulley from the top end.  To lower the tower, I loosen one nut at the bottom, two bolts holding a clamp that attaches the tower to a house bracket, put a little slack in the steel wire rope, give it a little push and then crank the tower over until the antenna almost touches.  Then I wedge a small step stool under the tower and transfer the weight onto the step stool (slacken the wire rope).  In the case of hurricane warnings, I can have my antennas down and safed, and then be back inside with my feet up in under 30 minutes.

The centerpiece of all that is the pipe.  See up there where I mentioned it was "schedule 40 steel pipe"?  In a region where humidity is one of our major exports, rust is your enemy that never sleeps.  I had my first rust issues within five years, and I've been fighting rust on it since about 1995.  I actually gave up and said I have to replace it a couple of years ago, but something always got in the way to distract me.  Now is the time.  Swearing I never want to work on rust again, I got an aluminum pipe.  I figured out how much the pipe I have should bend under 200 pounds of load, and then sized an aluminum pipe to handle that.  Then I got one a half inch bigger.  (The amount of bending depends on a property called the moment of inertia of the shape, which scales as radius to the fourth power so an extra half inch makes a noticeable difference). 

For much of the last month, I've been rounding up parts to rebuild everything, and just dealing with all the pieces that need to be worked on.  I spent a full week trying to get a stainless steel U-bolt!  The bolt itself was hard to find, and the one supplier I could find wanted to charge me $19.50 for one bolt and almost the same to ship it.  With a little delay, I was able to pick it up in town with no shipping charge.  I spent another week trying to find a replacement winch.  If you don't want the same old standard stuff every home repair uses: PVC or ABS pipe in small sizes, or a winch with a nylon strap, it gets difficult. 

While all of my antenna projects tend to begin with "when it cools off", the other side of that is, "I've got to get this done before it gets too hot again".  I should be good for another six, maybe eight weeks; after April 1st, it gets more iffy.  But this is one reason why I've been a bit "on again, off again" around here.
Some of the problem.  Rusting holes.  Rust around bolts.  That cracked area near the bottom is Bondo body putty.  I cleaned out the rust, wire brushed it and sanded to bare metal with sanding drums on my cordless drill.  Dried it, filled the hole with Bondo and painted over with Rustoleum.  Two years later the rust was pushing the Bondo out of the holes. 





11 comments:

  1. Is it a Universal Tower or an AlumaTower?

    WAAAAY back when I had my last tower, it was a Rohn 45G fold-over. The hinge was at the top of the first section, about 8' up, and the sections above that had a "boom" (can't remember the exact name...cantilever?) bolted to them that ran almost to the ground. My Dad and I measured carefully, and dug the base (4'x4'x6') so that when fully folded over, it all stayed in our yard.

    I got it used, for only $75, from a "Rich Ham" in Barrington, Illinois who was happy to see a "kid" get it. He even through in a roll of brand-new aircraft stainless cable to replace what was on the winch.

    Spent a LOT of the summer getting it wire brushed and primed, and then painted.

    It was a 65' model, and with the chrome-moly pipe, my Hy-Gain 2-element 40 Meter beam (also bought used and refurbished by me) was about 70' above ground.

    And I had a TH6DX on top of that....

    No tower here, but I'll probably get a 40' one when we move to Colorado.

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    1. It's an Aluma, and I got it new back when I put it up. They used to sell a Ham Special or some name like that; it's a 20' section of a light duty tower with space for a rotator and the hinge at the base.

      If I had the room, or my lot was better laid out, I'd go for a 45' crankup/tiltover.

      Delete
  2. Radio is going all digital.
    How is that affecting the ham world?

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    Replies
    1. Pretty much everything, top to bottom. Or not, depending on the operator's preferences; I mean there are still guys who get their kicks out of operating radios made in '50s or '60s. At the other extreme, there are guys with Software Defined Radios that are really a computer with some radio hardware attached.

      This could get long, because I'm having a hard time thinking of areas that haven't been affected by computerization. You might look at one of the pages listed in the right column down after Florida Gun Blogs; Privacy in Radio Communications" for some stuff on the use of computers for digital communications. Those are usually keyboard modes, not using a microphone.

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  3. Aluminum will also corrode here in Florida. Why did you choose to not go with a 10' stick of 4" schedule 40 PVC, and then fill it with fibered concrete?

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    1. I have a friend whose daughter is a civil engineer who said it won't be strong enough. My original idea was to just make a concrete square pole, like the FPL poles. Hammer together some boards into a 4x4x10' (or whatever size I need) concrete form and pour. She said it takes special pre-stressing. Whether or not she was right is beyond my meager knowledge of concrete.

      Trying to accommodate the galvanic cautions and keep the aluminum from corroding has been much of the effort I've been going through.

      Delete
    2. That's why I said "fibered concrete". If Blue is for you:
      http://www.lowes.com/pd_234137-286-100668_1z0udag__?productId=3026899&pl=1

      On the other hand, if you're and Orange Man:
      http://www.homedepot.com/p/SAKRETE-80-lb-Crack-Resistant-Concrete-Mix-65201090/100390848

      Cast inside a 10' chunk of 4" PVC, either should do fine, as long as you are careful to minimize voids while you "pour". Concrete on its own has very little tensile strength. Prestressing it makes sure it's always in tension, if done properly. Fiber has largely the same effect, as long as you don't let the loads get TOO high. Your application, which only carries a real load when raising or lowering your antenna, should be fine with just fibered concrete. INSIDE the PVC shell.

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    3. Interesting. I suppose it's not too late, although I'm left with 10 feet of aluminum pipe. Do you have any figures that would be like a Young's modulus I could crank into the equations for bending under load? My load at the end of 20 feet is about 80 pounds. I've always figured 100 but that's probably inadequate margin.

      My plan with the pipe was 3 feet in the ground, 7' sticking up. For the ground, I'm not sure how big a concrete foot to pour, but was leaning to about 1x1x3' deep. Do you think that's necessary for this post?

      We can go to email if you prefer: SiGraybeard at gmail dot com.

      Delete
  4. I would hit either here:
    http://www.sakrete.com/contact/

    or here:
    http://quikrete.com/ContactUs/Main.asp

    depending on whether you are Orange or Blue.

    The loads you are talking could probably be carried quite well with just the 4" schedule 40 PVC alone, but the concrete will provide additional factor of safety, and significantly increase the stiffness.

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  5. Any used sailboat masts hanging around in Florida? Seems like they would be good for height, and anodized for corrosion protection. Should need the shrouds since it would not be carrying a sail. Lightweight too.

    itor

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  6. aah - "should not need"

    ReplyDelete