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

[HansLG at aol.com]

You only have to climb a tower once to know that you want as little as  
possible "complications" once you are "up there". Also, it is not the top of 
the  tower that is exposed to stress, it's the bottom. The tower section 
"below" have  to take the mechanical stress from whatever is above. That's the 
reason you  design the tower from top-down.
 
Design the tower for the height you need and don't plan to add anything  
later.
 
Hans - N2JFS
 
 
  
____________________________________
 From: wc1m73 at gmail.com
To: xnewyorka at hotmail.com,  towertalk at contesting.com
Sent: 1/10/2012 6:50:08 P.M. Eastern Standard  Time
Subj: Re: [TowerTalk] How to get another 10' in height? Add a  mast or 
add another section?


I forgot to mention one of the more obvious advantage to  using a 10' tower
section instead of a mast: you can climb it with far less  "pucker factor"!
Seriously, it's not a lot of fun to climb a mast or drop  it to do
maintenance on the antenna.

73, Dick  WC1M

-----Original Message-----
From: Dick Green WC1M  [mailto:wc1m73 at gmail.com] 
Sent: Tuesday, January 10, 2012 2:55 PM
To:  xnewyorka at hotmail.com; TowerTalk
Subject: Re: [TowerTalk] How to get  another 10' in height? Add a mast or 
add
another section?

I went  with an extra 10-foot section. There are lots of advantages to  
that,
including not needing a heavy-duty mast if you set the top antenna  just
above the top plate. In fact, since you don't have a rotor, a short  piece 
of
pipe will probably do.

The tower is Rohn 55, 110' total,  including the extra section. It's guyed 
at
33', 63' and 95', with TIC rings  one foot above each guy bracket. The guy
points have more to do with  placement of the stack of antennas on the TIC
ring than available distance  to the guy anchors.

So there's 15 feet of tower above the top guy  point. I have a 12' aluminum
mast with 1/4" wall, seven feet below the top  plate and five feet above the
top plate. The mast supports a Cal-AV 2D-40A  (16 sq ft windload and 165 
lb.)
The boom-to-mast plate sits an inch or so  above the thrust bearing in the
top plate, so there's virtually no bending  moment on the mast from that
antenna. I recently added a 6-el 10m  monobander at the top of the mast, 
five
feet above the top plate. It's only  4.1 sq ft of windload at about 25 lbs. 
I
don't believe the monobander  presents any significant bending moment to the
mast. The mast is turned by  an M2 Orion.

I've climbed the unguyed portion of the tower many times  and it's pretty
darned solid. I have no worries about it withstanding the  20 sq feet of
windload above the guy bracket. Rohn 45 isn't as rugged as  Rohn 55, but you
should be able to find out if it'll handle the  spec.

73, Dick WC1M

-----Original Message-----
From: John W  [mailto:xnewyorka at hotmail.com]
Sent: Monday, January 09, 2012 11:23  PM
To: TowerTalk
Subject: [TowerTalk] How to get another 10' in height?  Add a mast or add
another section?


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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