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Re: [TowerTalk] Basic Help Needed

Subject: Re: [TowerTalk] Basic Help Needed
Date: Wed, 24 Aug 2011 13:23:31 -0400 (EDT)
List-post: <">>
In a message dated 8/24/2011 7:49:28 A.M. Pacific Daylight Time, writes:

>  My first project is to get a tribander (10, 15, and 20m)  up and on the 
as quickly as possible.  I have selected a ROHN 9H50  telescoping mast that
extends to 50? and has guy mounts at 4 locations up  the mast.  ROHN
recommends each set of guy wires start at 30? from the  base of the mast. I
have bought a pair of Chicago Grips for tensioning the  guys and a LOOS
tension meter for setting the guy wire tension to 10% of  its maximum

>  I thought this would be an easy  project (even though I don?t have any
experience in erecting towers).   But, it hasn?t turned out to be so easy
when I realized the projected area  of the tribander I have chosen is about 
sq ft of projected area (EPA),  but the footnotes for the mast say the
antenna load should not exceed 2  EPA!  When I add 1 sq ft for the rotator
and mast to support the  antenna, my EPA is over 5 sq ft!

Hiya, Wayne --

    Yes, it's inadequate for your application. And  yes, it's not easy to 
put up. 

>  So, my question is:   should I abandon this project or can I make 
changes in
the support of the  mast so my tribander can stay up even in the 100mph area
max wind speed  estimated for my county?

Ouch. 100 MPH is significant and only a tower  will handle what you're 
proposing. And not a crank-up.

>  What  I have thought of changing is: 1. Not using the ROHN recommended 
wire  as the guy wire but going to ROHN 3/16 EHS, 2. Using the software
called  MARC (Antenna & Rotator Calculator) to calculate the required  steel
alloy and thickness of the antenna mast, 3.  Limiting the  antenna mast and
rotator to only 2 ft above the top of the telescoping  tower mast, and using
4 guys instead of 3 (for a total of 16 guy  wires).

Changing guy wire strength won't change  anything. The limiting factor in a 
tower is leg strength, and since you  basically have one leg in your mast - 
the leg strength is the same regardless  of what you're using for guy wire. 
(Using a heavier guy wire will also add  more compressive forces to your 
mast, thus lowering the capacity even  more.)

>  Can I make this mast stand up?  
    Sure, but only until the first big wind. 
>  What are the weak areas and how can I make them  stronger?  
    You'd have to re-engineer the whole thing which  would entail beefing 
it up. Is it worth it? Probably not.
>  Would you direct me to books that discuss tower  supports?

In my tower book - UP THE  TOWER, The Complete Guide To Tower Construction 
- I have a whole chapter on  antenna support selection. (available from 
_www.championradio.com_ ( )
        Your mast won't work with  your big winds. A good choice might be a 
self-supporting roof tower (e.g. Glen  Martin Engineering) but when you're 
working with potential 100 MPH winds, it'll  probably just rip the roof off. 
Your best bet is a real tower designed for your  application and parameters.
Steve     K7LXC
Professional tower services for hams
Champion Radio Products
PS - If you want the REAL skinny on tribander performance, I'd also suggest 
 our tribander comparison test also available from _www.championradio.com_ 
( . 

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