Tower bracket for antennas by AK2O

Tower bracket for antennas by AK2O

"Wimpy" brackets are okay for house installs and where ice loading and winds are not a factor. For the mountain tops, however you'll need a real bracket. For this prototype the author used mild steel, in .188 thickness (that's 3/16"). After lengthy testing on the bench and on the tower (in the HOT sun) with trail and error, the author came up with a nice design. After many tries (in past versions), the author cut, cleaned, welded, and painted the parts for this type of bracket. The first part is a 3" channel pair that "grabs" onto a tower leg of substantial diameter. Then the two horizontal cross bars extend out, away from the tower leg. The author added a 45 angle bar to add strength to the top cross bar. Using 2" sch. # 80 pipe, I welded on two pieces of 2" x .188 angle metal onto it, so bolts can be secured from it to the cross bars. I keep the holes close to the corner of the "L" metal for maximum strength. The main reason for the "L" metal, is that the angle of the pipe, now will be adjustable several degrees. Most "microwave" towers use 3 or 4 legs and some of them angle inward a few degrees. Unless you know the angle (at this remote, far away site) it's best to drill (at least) a couple holes, spaced 1 1/2" apart (on the lower bar), so you can quickly adjust the bracket for level, once it's mounted on the tower. The author did set the first angle hole for "0", for the towers with straight vertical legs. Here's the overall bracket. On the right shows how it grabs and secures on the tower leg. The leg can be of different diameters, while the bracket still can "grab" or secure itself. The only observation and inventory/install change will be the length of the bolts. For example a tower leg of 3" O.D. will need bolts of 5 1/2" in length. You also have the choice of bolt size (diameter) and grade. For this prototype the author selected 5/8" bolts in grade 2. This is the first feature. If you know what the angle is you could skip this section and make it fixed, and just weld the pipe directly to the cross bars. The main thing is to provide a solid mount for the antenna(s).









Here's closeup on the adjustable part. The picture on the left shows the top bar uses a 3/4" bolt for the swing point, and to add some strength a 5/8" bolt was added, that works through a elongate hole, so it can swing into it's final angle position. Because of the tight clearance to the corner of the "L" metal it was necessary to grind off a flat spot on the two flat washers. The right picture shows the bottom bar.

The author's other designs had a problem. Here's the explanation. When you "swing" the pipe, with a "fixed" hole on the bottom, because of the 'arc' of the "swing" the lower bar hole(s) would follow a curve of this 'arc'. That would require the lower bar to be very wide. The most suitable metal for that would be more of the 3" wide "C" channel metal. However, because of the shape of this channel metal you could not easily use a wrench, inside the channel area. (you would have to use a large socket). Also only one side of the channel could be used to mount (being a flat surface). For both solutions, the Author used square tubing for both cross bars, of .188" thickness. And, instead of the 'arc' hole having to follow the swing, the lower "L" metal was made, with an enlongated hole, or slot, so the bar holes can be in line (in the lower bar) and the bolt position moves vertically to meet that bar hole, within the 'arc' swing. WORKS GREAT !! The best way found to make this slot (since a plasma cutter was not available) is to notch the "L" metal, then weld an addition piece of flat steel on the outer edge, thus, making it a little wider, with the slot. 3/4" bolts were used on this part, as well, so the pipe is secured with a total of 3 larger sized bolts. As mention previously the "C" channel (onto the tower) are (typically) 5/8"; 4 of them, squeezing the two halfs into the tower leg. The channel metal has 2 contact points to resist twisting, as well. This will provide a strong extension, out from the tower leg. With 300 pounds of ice loading, plus, extending away from the tower will product enormous weight stress on the bars, therefore, they need to be very stout. Should you be concerned about extreme cross wind/ice loading, you could add a strut from the pipe to the side of the tower.









The left picture shows the complete bracket, in the "0" angle (vertical) position. I don't like to drill many holes (ahead of the install) in concern of weakening the lower bar. To assist on on-site last-minute possible drilling I did drill several small pilot holes to start the larger 3/4" hand drill bit. Remember to bring some cutting oil, which greatly extends the life of the bit and is easier to drill by the operator; YOU. On the right, shows the pipe is swung in "two" positions (2 holes, spaced 1 1/2" on center) therefore, has a angle offset of 3". Knowing the height of the cross bars (about 27") will give you the 'arc', or angle if you need to know that in advance. For the last tower (prototype) project I did recently the tower angle only needed the one hole, therefore, had an angle offset of 1 1/2".









Want to know a slick way for a movable mount? If you swing the mount, you'll need to either make multiple hole in the bar, or do a elongated (slotted) hole for the bolts. First, start with another piece of angle and notch it down about 3/8", with 1" ends left full depth, for strength. You can judge by holding the bolt, you plan to use on the edge .









Then cut a piece of flat the same length of the angle and hold it up, with the both for just a little play. .









It's important both pieces are flat, so they run across the bar, nicely. One way to keep 'em flat while welding is clamp them against a flat surface, such as a piece of hard particle board. After that, clean up the areas from cutting oil.









Clamp the other angle brackets to the pipe to provide a stable welding surface .









Here's the top swivel section. As you can see the lower part of the slot is wider for the arc .









and here's the bottom section showing the slot will "follow" the arc swing .









Here's some of the tools you'll need for the project. That oil can in the foreground is for cutting oil, which saves both saws and bits many times over and makes cutting and drilling easier, too. Grind clean the areas to be welded, to make nice ones, like this .


















This may be copied in complete form only for non-profit purposes, such as for the knowledge for the Amateur Radio Service, with AK2O credited as designer. For other arrangements please contact the author.

Copywrite: AK2O 2004

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