[TowerTalk] Making an insulated base for 80 meter vertical from Rohn 25

[Roger (K8RI)]

I haven't read all of the replies yet, but Teflon is a poor structural 
material. If under compression or expansion it will move.  It "cold 
flows" substantially, like an extremely thick taffy.  I used it for the 
base insulator on a mobile antenna.  In less than 20 miles the antenna 
was swinging around at almost a 45 degree angle.  I had to stop and guy 
it into the car through the windows using heavy fishing line.

Delrin, or the strongest ...fiberglass painted with a UV protecterant 
should work fine.

73

Roger (K8RI)

brahmangou at aol.com wrote:
> Hi Guys,
>  
> I got a few emails asking where I got the insulated base. I made it. The  
> insulated legs on the market are pretty expensive, and I didn't like that 
> they  are in tension and compression when the tower moves with the wind and 
> under  other external forces. It appeared to me, and I may be wrong, that the  
> insulating material might not be as strong/durable as the original tower  
> legs.
>  
> I bought a  1" thick 24" square HDPE cutting board from a commercial  
> restaurant supply , about 18 dollars, and drilled it to fit over the  j-bolts in 
> a standard Rohn 3'x3'x4' concrete tower base. I put the Rohn  tilt base on 
> top of the cutting board. There are several machine shops on ebay  that sell 
> PTFE teflon machining end pieces, leftovers. I bought a couple of  short 1 
> 1/2" teflon rod pieces, 6 dollars, and drilled/turned them to fit  in the 
> annular space between the bolt holes in the tilt base and the edges of  the 
> j-bolts as insulating bolt sleeves. Then I took a short piece of 3" teflon  
> rod, 3 dollars, and sawed 1/2" thick disks off of it. I drilled through the  
> disks and made insulating washers for each of the base bolts.
>  
> This way all of the plastic parts are always in compression, at their  
> strongest. I used teflon for all of the parts that are exposed to the sun to  
> avoid UV breakdown of the insulators, also teflon is a superior insulating  
> material for the thinner (3/16" thick) bolt sleeves. By using the tilt base, I 
>  can lower the tower to make adjustments and repairs in the future ( not 
> getting  any younger, hi hi).  I'm ready to install install the tower sections 
> and  run the feed line as soon as the weather clears up.
>  
> Marty Haley AB5GU at ARRL.NET
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