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@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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|