[TowerTalk] Self-Supporting Rohn 45G

Bob Smith na6t at na6t.com
Mon Apr 30 12:07:40 EDT 2007


HI Dale,

According to Rohn's specs for the 45G tower you can have the following:
NO ice

30' self supporting tower       12sq ft of antenna
35' self supporting tower       8.7 sq ft of antennas
40' self supporting tower           5.1 sq ft of antennas

this is off their website.  It's a llttle hard to find because it's 
in the 25G section under
the on-line catalog in the section called "Allowable Antenna 
Areas.   Hope this helps.
I've also sent you a copy of the pdf to your personal e-mail address.

73's
Bob

Robert Smith Consulting
"Wireless Installations -- Government, Businesses & ISP's"
F.C.C. Licensed-Commercial & Amateur Services
A.R.S NA6T
ARRL Life Member
1-707-964-4931 w/answering machine
Fort Bragg, California   95437

"On The Air-Conditioned Mendocino Coast, In REAL Northern California"
No trees were destroyed in the sending of this message.
However, a large number of electrons were terribly inconvenienced.
NA6t

Message: 10
Date: Mon, 30 Apr 2007 09:09:37 -0500
From: "Dale Martin" <kg5u at hal-pc.org>
Subject: [TowerTalk] Self-Supporting Rohn 45G
To: <towertalk at contesting.com>
Message-ID: <001501c78b31$323bb2a0$6401a8c0 at DESKTOP>
Content-Type: text/plain;       charset="us-ascii"


For many years, the JSC Amateur Radio Club station at NASA's Johnson Space
Center in Houston, used an un-guyed Rohn 45G tower consisting of one
straight section and a pointy-top section as it's satellite antenna tower.
The tower straight section had steel 'tabs' welded to the mounting sleeves
at the leg bottoms.  The tabs mated with corresponding tabs on a base plate
bolted to bolts imbedded in a concrete base and served as a tilt-over
mechanism--only used when we installed and removed the tower.

With the demolition of the building housing W5RRR, the SCUBA club room, and
the employee's recreation center grounds maintenance building/garage, the
tower had to be removed.  A new building will go up in that space and will
again house W5RRR, Lunarfins, and the grounds maintenance staff & equipment.
A new tower base will be put in place next to the building for the satellite
tower/antennas.

However, the building will be taller, necessitating adding at least one more
section to the old satellite tower--I don't know the new roof elevation.  We
cannot attach the tower to the building.  With the tower concrete base next
to, but not contacting, the building slab, there is no room for proper
guying.

I've done some looking around to find windloading for the antennas we are
using (I don't have the doc's -- they are in storage during the construction
period), but they are a 2m 24-element and a 70cm 36-element (both circular
polarized) antennas.  I didn't find the same antennas (24- and 36-el's)
listed in the three or four antenna manufacturer webpages, but from the
specs for the biggest 2m/70cm satellite antennas, it looks like windloading
won't be more than four or five square feet.  How much should I add for the
AZ/EL rotator?

With the added height requirement, I'm considering changing the base to an
imbedded base section with two straight and one pointy-top sections.

Is it safe to freestand a 28' Rohn 45g with 4-5 sq.ft. of antennas on top?
With real beams (C4, TH6DXX, A4, 204ba, etc.), I woldn't consider it.  But,
for these two 'lightweight' antennas?

Thanks in advance for any info, guidance...

73,
Dale, kg5u








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End of TowerTalk Digest, Vol 52, Issue 78
*****************************************

Bob Smith
A.R.S NA6T
ARRL Life Member
Fort Bragg, California   95437

"On The Air-Conditioned Mendocino Coast, In REAL Northern California"
No trees were destroyed in the sending of this message.
However, a large number of electrons were terribly inconvenienced.




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