W7rca Ham Tower Extension Build

[quiet tiger]

Hello all,

I have been pretty quiet on the forums and this will be my first project posting.

I thought my latest project, a tower extension for ham radio antenna tower, might be of interest, in terms of material properties and selection, engineering design and fabrication. However, there is no lathe or mill work involved however, mostly fit-up, weld up and general fab.

The project will be to build a 32 foot tower base for a 54 foot crank up tower purchased from Tashjian Towers. The crank up tower, 19 3/4 inches at the base, is 21 feet collapsed and 54 feet extended in three sections. It is designed to attach to a concrete base and weighs 600 pounds.

Instead I'm going to add 30 feet ( for a total height of 84 feet extended), attaching that base to a 30 foot extension and that is this project.

I already have a 51 foot tower in place that tilts on a hinge I fabbed from old tractor parts.

The lower 8 foot section of that, fabbed from 3x3x3/8 angle, will be re-used as part of the 32 foot new base build.

I will also re-use the hinge, beefing that up for the added weight and wind load.

The overall design must withstand the 80MPH (1.5 times that for safety) gusting limit for my area ( 26 miles east of Seattle).
The reality is, in our Cascade foot hills I will never see 80MPH gusts, but that is the engineering standard.
The 54 foot Tashjian Tower is designed for 80mph gusts of 3 second duration at its full height. At full collapsed it can withstand much more.

I will post a picture of the current base for reference, here we go.............must be done by Sept.

 

[brino]

Hi quiet tiger,

I am _very_ interested to see this project. The crank assemble, the base, everything.

At 21 feet collapsed how do you raise that? A crane?

I am always interested in ways to move/lift/raise heavy things.

Thanks!
-brino

 

[Patrick]

Quiet Tiger, sounds like a good project you're getting into. What are your plans for guiding the sections as you raise the addition sections of the tower? 84 feet is a long way up with alot of wind loading, but then I am not familiar with the weather in or around Seattle. I had a 52 ft. free standing Gearald tower which was a tapered tower here in Wisconsin and when the wind would blow hard it would sway just a little. Anyway, keep us posted on your progress, I for one will be following.
Best Regards
Patrick
N9CWK

 

[quiet tiger]

Thank-you Patrick and Brino for your interest and questions.
I guess I need a few more posts before I can post any pictures.

Brinos question as to how the tower extends and collapses, it is via an aircraft quality steel cable and pulleys, using a hand or power winch at the base. The cable reeving and pulleys are what allows the tower to be raised or lowered.

Just imagine a straight piece of line attached to the top of a 21 foot 3 legged tower, looped down inside of the three legged triangle,to a pulley at the base of the 2nd section inside, then back to a pulley on top of the outer section ( creating a big vertical loop) and again back down to the base. At the base, pull on the line and it raises that middle section. ( picture worth 1,00 word there but cant post yet)

The 21 foot / 84 foot section I purchased already built by Tashjian Towers, here is link: http://www.tashtowers.com/crank-up-towers.php

The model I purchased is the LM354. It is that "crank-up" tower that I will fit to the top of my fabricated vertically static 32 foot base.

For Patrick, yes 84 feet is a long way up for free standing. My wind load at that height is restricted to 18 sq feet (at 80mph 3 second gusts) but my antenna load will be 12 square feet, so some margin of safety.
Collapsed the tower will be 51 feet high, 84 feet high fully extended.
90% of the time the tower wont be extended past 70 feet ( the why is all Ham radio speak, so wont expand on it here)

The very bottom , base currently ( current 51 ft free standing tower) is 38 inches wide between each of the three legs, tapering to 14 inches at the top section.
That existing tower has an 8 foot base section I fabbed and connected a free standing 43 foot tower to get the 51 feet height.
That 8 foot base section will get re-worked / reused for the new build of an additional 24 feet to get a total of 32 feet. ( the LM354 will fit 2 feet down into the top of that 32 foot base for a net total of 51 feet collapsed, 84 feet fully extended)
The new build will taper from about 28 inches ( at the top of the 8 foot base) to 20 inches, where it intersects with the LM 354 base of 19 3/4 inches.
So total will be 38 inches at base tapered to 14 inches at 84 foot height.

The base is 6x6x4 foot re-enforced concrete buried to 4 foot depth.

Will try to get some pics of exiting base posted soon.

Im off to cut plate for the feet of some sections.

Best Regards
Rich
W7RCA

 

[quiet tiger]

OK, I was wrong, I can post poics, here is existing tower base with tilt over boom installed, hinge at base fabbed from tractor parts.