Building a Dirt Base for Small towers

Disclaimer:  This is what I have done. It should not be taken as a suggestion, or recomendation on how to build your own bases, or even condoning such. Always seek knowledgeable guidance when doing tower or construction work.  Tower climbing is dangerous even for those of us who have the training and have done it for years. 

Do NOT USE A DIRT BASE ON TOWERS THAT ARE NOT PROPERLY GUYED!

SAFETY NOTE: Adhere to proper safety practices, do not use machine tools unless you are thouroughly acquainted with and are proficient with their use. Wear proper eye protection. Do not wear loose fitting clothing, or long loose sleeve shirts that can become entangled in the machinery. Do not work alone.


The purpose of the base for a guyed tower two fold.  It keeps the tower from sinking into the ground and it keeps the bottom of the tower from moving sideways. Conversely the base for a self supporting tower must be far more massive as it not only prevents the tower from sinking, but it must be massive enough to overcome the overturning moment of the tower in strong winds. The bases for self supporting towers are not only far larger than those for guyed towers they are also more complex and depend on "re-rod" to reinforce that base to prevent the base from losing structural integrity.  In both cases much depends on the type of soil and the soil conditions as to the size, mass, and design of the tower base.  

Always follow the tower manufacturer's directions.  

I'm intalling a small ROHN 25G on the West end of my shop.  This tower will support a relatively small weight and wind load at 50 feet. The tower is also bracketed to the eves of the roof near the peak as well as being guyed.
It should be noted that the building is of much stronger construction than a typical home. Due to the relatively short tower (50 feet) and light load (C19XR tribander) from weight(~60#) and wind load (~12 frt^2) I chose to use a dirt base.  Note: My soil is capable of supporting the tower base. To be sure other soil would do so would require a proper soil analysis.

This article is meant to be informative, not a "do-it-your-self" on how to build and install a small tower. 

Again, I reiterate, "Tower Climbing is Dangerous" even for professionals.


As I stated in the article about building adapter plates, I had to take the antennas down and decided to replace the tribander and put it in a more accessible location. Hence the 50 foot, ROHN 25G tower installation on the West end of my shop.

I chose to build a heavy duty dirt base, 5 feet deep. The legs are 1inch solid steel rod, with tabs welded on one end to form the hinges and atach points.  The side plates are 6" wide, 1/8" steel.    To get the proper leg spacing, I set a 10' tower section onto an 18" square of 3/4" plywood, and marked the leg ends onto the face of the plywood.  I stacked two sheets of the same size and then drilled out the one inch holes for the legs.

This shows the three legs of the base inserted into the plywood templates with the tower section in the background.

The base was leveled and propped in a position to make welding the side plates into position relatively easy.

The plates on one side "tacked" in place.

 

 

 

 

The base was primed with self etching primer and then painted with a high quality Acrylic.  Not the best welding job, but it's strong. Also with the solid legs moisture and interior rusting is not a problem.

 

A enlargement of the top of the previous photo showing the hinge structure made from 1.5" X 5" X 1/4 inch steel.  The pieces were clamped in a vise so the holes would be in register. Bolts with spacers were added and they were bolted to the tower bottom section. Then both the base and bottom section were leveled and aligned before the tabs were welded to the base section legs. 

The partially completed bracket. Note the angle that matches the roof angle. also the clamps to the tower legs are "saddle clamps" and not just U-bolts.  I'll have detailed photos of the base and bracket in place later (If I remember).

Total cost including paint is just over $30 and I have enough paint and primer to do many projects.

 

 

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