[TowerTalk] How to get another 10' in height? Add a mast or add another s...

[TexasRF at aol.com]

Hi John, as already mentioned, the 80% guying is subject to change with  
proper backup calculations.
 
Also, the forces on 72 ft guy spacing will be very similar with a large  
antenna at 110 ft using a mast vs another tower section. Most of the added 
load  is the antenna; not the last 10 ft of the supporting structure.
 
Also mentioned was the strength of a 45G section as much stronger than a  
mast. That is not entirely correct as masts can be engineered for strength as 
 well as tower sections. For example, a 3" OD, .25" wall 1020DOM steel mast 
will  safely hold about 35 sq ft antenna load 10ft up with a 90 mph wind 
speed. A 45G  section would be good for about 40 sq ft. If the mast was 
upsized to .375" wall,  it would hold a 48 sq ft wind load.
 
The cost of 3" OD mast is not trivial. By the time galvanizing costs are  
added, the cost of an additional 45G section will be a bargain. Even more $$  
will needed for the custom steel mast to tower mounting brackets. 
 
Since the tower is in the planning stage, now is the time to consider  
making it 55G. The added capacity might prove useful later on.
 
73,
Gerald K5GW
 
 
 
 
In a message dated 1/9/2012 10:23:29 P.M. Central Standard Time,  
xnewyorka at hotmail.com writes:


If I  have a Rohn 45G tower of a given height, let's say 90', guyed per the 
Rohn  book, and rotating from the base, hosting several side-mounted yagis 
for 10m  (3), 15m (2), and 20m (1), and I want to add another antenna up at 
100' (a  small 40m 2L) that also rotates with the tower, which one is the 
safer/better  installation:  adding a mast that protrudes 10' above the top of 
the  tower (and for some distance down into the tower), or adding another 
10'  section and sidemounting the new antenna at the top of it?

This is a  theoretical question, because I haven't built the tower yet, but 
I plan  to.  

The first reply many might have is probably: Why don't you  just build it 
to 100' per the book, instead of 90'?
The answer to that is  that I don't have enough real estate to put guy 
anchors 80' from the base, I  only have 72' available.

Also, I have not even seen hardware that  allows adding a FIXED mast at the 
top of a Rohn tower - sort of like a thrust  bearing that can't turn. How 
is this typically done?

Thanks &  73,

John
W2ID

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