The 80% guy radius is just a manufacture's recommendation. It can be
smaller, however this puts more stress on the guys and tower and it
probably reduces the wind load rating. You can also use elevated guy
anchors which effectively increases the anchor radius. As an example, at
P40A, http://www.qrz.com/db/p40a , I used a 35' (elevated) guy radius on
two anchors for a 70' Rohn 55g tower. Of course any changes to the
manufacture's design should be approved by a PE.
73,
John KK9A
To: towertalk@contesting.com
Subject:[TowerTalk] Reduced guy radius for Rohn 45G tower
From: Avery Davis
Pardon me if this is a dumb question for my first post to this list, but
this is my first real tower after many years in Amateur Radio.
I came across a great deal on a lightly used Rohn 45G: six sections
plus a top section. The problem is that my lot is not really big enough
for the 56 foot guy anchor radius recommended in the Rohn brochure. I
am looking for suggestions as to what I can do to make this smaller.
For example, I could put up just a few of these sections with no guys.
The Rohn 45G self-supporting tower brochure has a table for 90MPH (which
I understand is required for my jurisdiction, although radial ice is
not), but this only allows 30 feet height with 4 sq.ft. This is smaller
than I would prefer, which is nominally about 10 sq.ft., but the Rohn
brochure puts me at only 20 ft. height for 11 sq. ft. So, what can I do
with these tower sections to get more than 30' height and 10 sq.ft. in a
radius less than about 20 ft.? Would it help to use three sections as
elevated guy anchors? This would leave me three sections plus the top
for 3x10 + 8 - 4 = 34'. How do I determine the wind load allowance for
this configuration?
Or, would you recommend I just resell the 45G and buy a genuine
self-supporting tower?
73,
Avery, WB4RTP
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