i e mailed a guy jerry that built one heres his story....[ham radio]
Well, let's see. In 1976 or so I was living in Missouri and wanted to build a tower to place a ham radio antenna on. Maybe you could learn my mistakes. I used 3/4-inch EMT electrical conduit. It is available from electrical supply stores, Home Depot, etc. It comes in ten foot lengths. I used the full ten foot lengths for the [mostly] vertical parts. The base was 5 or 6 feet on each of the three sides. Then the triangles above the base were 4 ft on each side, 3 foot on each side etc. The top one was 1 foot on each side. To fasten the conduit pieces together, I took a hammer and flattened about 1 1/2-inch of each end. Then drilled a hole in it for the bolts, and finally bent them so that the flat ends would be parallel with each other. I assembled the tower (which is almost 40 foot high) on the ground. Dug three holes and placed some more conduit into the holes. Using u-bolts I was able to make a hinge. So, with a neighbor helping me, we walked the tower up and in a vertical position. Bolted it to the third anchor. Of course the anchors were concreted into the holes in the ground. To make it plumb you need to get the base level which is easy enough with a builder's level. To get the antenna on the tower I used a section of aluminum ladder with hooks on the top end to climb the tower. I had a 2 ' steel mast, a rotator to turn the antenna. This antenna is called a cubical quad. Most of the members are fiberglass so the weight isn't very much.
It worked well for a few months.
One winter night the wind came up in a snowstorm. I thought I heard a crash but not until morning did I discover that it had "folded" between the base triangle and the one above it. The failure is that the conduit, which is sometimes called "thin wall conduit" simply wasn't stiff enough. It isn't designed for structural uses, only to enclose wire conductors inside buildings. There are better materials available but, of course, this would raise the price. There is, for instance, rigid conduit. When used, rigid is often threaded at each end for connections to elbows, tees, or fittings for enclosures. It also is heavier. Another issue is how the ends are fastened. One of the neatest fasteners I have seen is designed for scaffolding. There actually is a family of fittings, some of which allow two pieces to be fastened together but then swiveled, so any angle you want can be accommodated. Another approach would be to use structural steel for the members and weld them into place. A AWA-certified welder could advise you on this.
I am a retired safety engineer so I advise you to use good design practices for any tower you are interested in. You also need to consider windspeed designs for your geographical area. The design will need to consider the tower wind loading plus anything attached to the tower such as an antenna, wind turbine, solar panels, etc. This data is available on the internet for the US by county. Consider using a mechanical or structural engineer at the design stages. You may be required to get a building permit. If you do follow this path, the code person may want you to show that the design has been reviewed and stamped by a PE in your state.
Good luck to you ... but play it safe.
