[TowerTalk] vertical mast calculations

[Jim White, K4OJ]

I have sorta been following this thread, it seems to me that using HF 
tapered element components and boom sized tubing with adapters you 
should be able to construct a vertical that does not have to be fat at 
the top...these 3" all the way up jobs are huge!

At least I hope so - I have been saving pieces and parts from HF 20 and 
40 meter elements thinking they would be useful in a four square array 
for 80 some day... I had envisioned one or two section of Rohn 6 or 
similar lightweight tower as the bottom and then 2" tubing dropping down 
to the 40 meter Telrex elements to get up to around 66 feet...

The only part of the project that seems hard is insulating the tower 
from ground - I refuse to pay for the turned fiberglass pieces that 
several market for Rohn legs, it seems like a foldover base which mounts 
to a product like "plastic lumber" which in turn is mounted to a buried 
base should do the trick.

My question is how good/poor a conductor of RF is the recycled pop 
bottle "plastic lumber" is... it is available in "4 X 4" size and I 
would think I could carriage/machine bolt a tiltover base to it and that 
in turn would be bolted to a small concrete base...

The goal is to have the elements completely free standing - no mid-point 
guying, etc... I may have the opportunity to put something like this up 
in the neighbors field adjacent to the QTH but will have to go with 
buried ground system since the cows that graze there can not get 
entwined in elevated radials.


SO - Towertalkians am I dreaming or is this feasible - it sure seems 
like the tubing portion of the elements should be fine - if they can 
withstand being horizontal continuously they certainly should be able, 
if mounted with even heavier tubing and then tower below them to stand 
"on end"...

Thanks in advance,

Jim, K4OJ

Remember: 34 days until the Florida QSO Party, check it out at: 
http://www.qsl.net/fqp




Dave Hachadorian wrote:
> 
> On Sun, 23 Mar 2003 09:15:24 -0800 "Jim Lux" <jimlux at earthlink.net>
> writes:
> 
>>I just ran across the following QEX article on the ARRL web site:
>>http://www.arrl.org/qex/1123.pdf
>>
>>It gives all the necessary design equations, etc. for unguyed 
>>towers.
>>
>>The article references an excel spreadsheet available as well.
>>(http://www.arrl.org/qexfiles/) look for Travanty.zip
>>
>>Jim, W6RMK
> 
> 
> Thanks a lot for that tip. The spreadsheet is very easy
> to use, and imported fine into Quattro Pro. It includes mast
> bending moment calculations. It was fun to crank the tower
> up and down, and vary the windspeed.
> 
> The main assumption though, is that the failure points are at
> either the tower base, or the mast at the thrust bearing. If
> there is an unusually weak link in the tower, other than those
> two, the spreadsheet is not valid.
> 
> Dave Hachadorian, K6LL
> Yuma, AZ
> 
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