Broadcast Tower bracket for antennas by AK2O


The basic difference between the first bracket article and this one is the latter is non-adjustable for angle. Most Broadcast towers (FM, TV, etc.) use a straight three or four legged tower. Incidentally, most of them are guyed as well, which is almost irrelevant to this article, and only for general reference.

"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. The bracket's based on "C" channel steel of 3" wide, 1 1/2" high and .250" thickness (that's 1/4"). The eight "L" angle pieces are also 1/4" thickness. The pipe is Schedule #80 2 7/8" outside diameter. As you can imagine the bracket is pretty stout. The "C" channel "grabs" onto a tower leg of substantial diameter, say from 2 1/2" to 4", or even about 5" if needed. For large diameter legs, then just increase the "C" channel with to 4" or wider. This version is made with three horizontal bars to extend out, away from the tower leg. The bars are .188 x 1 1/4" tubular. Then the 2 7/8" pipe is welded to the ends of the bars. One additional 45 piece was added to increase the strength to the bars, made from .120 flat steel 1 1/2 width. 5/8" holes were drilled at 6 3/8" apart, O.C., into the 4 sets of (2 pieces) "L" steel, 2 1/2" x 2 1/2" x .250" angle metal. The holes are 1 1/2" in from one end, to start with and whatever works out at the other end of each "L". It's pretty close to the first end. Then, these pieces were welded onto the "C" channel. The last set is for the top support bracket. The 8" long, grade 2 bolts through these holes will clamp pressure of each half of the bracket onto the tower leg. There is enough bolt length for a lock nut as well. (2 nuts per bolt end). This is for 4" legs. The "C" Channel will work satisfactory up to a 5" tower leg, however, you'll need to increase the bolt length to accommodate the lock nuts (2 nut per). Respectively, for smaller legs, will require shorter bolts. For example, a rough guess for a 3" leg would need bolts 5 1/2" long. Check to be sure on this one. As usual, a top mini-bracket is also made to support the upper portion of the fiberglass antenna. Two more pieces of "C" channel (same stuff) around 6" (can't remember) long, with the "L"'s welded on them, plus a piece of tubular welded out 90* angle provide the top bracket. The tubular is 16" of 1" x 1" x .188. Then 2" ABS pipe with a "T" is clamped on using #48 hose clamps. The antenna will run through the "T" ABC pipe. That way no metal gets too close to the antenna as not to affect the pattern. Use more of same bolts and nuts. 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 first picture shows the antenna bracket (not to be confused with the tower bracket project, here) from Sinclair. They will work ok with pipe up around 3" OD. The next picture is the "top bracket", with the tubular going out 90* from the bracket. The ABS pipe will be clamped on here, to extend out to the antenna. The third picture shows the "main bracket", as it would appear on the tower leg. This a some of the other pictures may show the two halfs not to line up. That's because they were (accidentally) taken with the bracket upside down. When properly mounted they all should line up for a good mount. The last picture is the "slave", or other half of the main bracket. Cold (zinc) type galvanizing paint was used, due to lack of time to get them hot dipped.

 

 

 

 

 

 

 






The first picture is a another view of the "slave" part. The other 3 pictures are other view angels of the main bracket. Reminder: for a larger version click on the image(s).

 

 

 

 

 

 

 







Here's a few drawings for the spec. The first one is not for this bracket, only to (better) show a perspective drawing on an earlier (prototype) version of tower bracket. In that version only 2 sets of bolts were used. For this project (version) emphasis was made for strength. The last two images are for this version.

 

 

 

 

 

 

 











Incidentally, if you need to mount an antenna on the side of a concrete building, wall, etc. you need the type of bolts to hold a bracket into the concrete. There are bolts available at your local hardware store. For more information click HERE.









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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