[grc] Hurricanes and antennas

[Eugene Beer]

Max.

We have  4 sections of Rohn 25 tower where only the bottom section is
secured (to a 1-storey concrete block building and a base concrete pad).
The highest  section is the shorter Rohn "Top Section" that tapers to a
canonical point with a short sleeve pipe in the middle. Then we added a
skinny aluminum pole that extends above the top section by 15 add'l feet.
So, the total height is about 50'.  We only use this tower for a lightweight
yagi antenna for receiving FM.  The center of mass of the yagi is pretty
much at the vertical mounting pole attachment (as is, I expect, your Comet
whip antenna's center of mass).

I would not try mounting a one-bay  transmit antenna (typically, 15-25 lb)
on our tower because of the weight, and because the center of mass would be
one or two feet out horizontally, thus exerting a torque moment on the
tower.

To maintain the yagi we've climbed the tower several times with our feet at
the bottom of the 4th section. We've experienced some slight jiggling of the
tower, so  to be on the safe side we recently added a 15 ft. strut to brace
the third tower section to the building.

I could get you a photo if desired.

Eugene Beer
Chief Engr, Columbus Community Radio Stations



-----Original Message-----
From: grc [mailto:grc-bounces at maillist.peak.org] On Behalf Of Max via grc
Sent: Thursday, September 14, 2017 6:11 PM
To: grc at maillist.peak.org
Subject: [grc] Hurricanes and antennas

I am looking at upgrading my antenna height ASAP as cheaply as possible ...
Aaaand the hurricanes are getting stronger!

So I'm interested in hearing stories of antenna mounting and tower/mast/pole
failures and how close can I push the envelope without ripping it.

Currently I have a 38' wooden utility pole with a Radio Shack extendible
pole like typical for TV and FM consumer Yagi antennas - which i topped with
a Comet 5/8 whip antenna.

I am pretty sure that a two Bay circularly polarized probably won't work on
that but I'd be interested if anybody has tried that!

So I've seen several examples now of Rohn towers with more than one segment
above its highest attachment point and with no guy cabling.

I've seen that height vary from 3 to 5 segments (10' each) above their last
attachment point.

I was hoping I could attach my Rohn Tower to the existing wouldn't utility
pole as its highest attachment point.

So in y'alls experience, how many 10ft segments of Rohn 25 can I go above
the highest attachment point as a bracket attached to something else like a
building for far I would have to have guy cabling?

Have you ever seen anyone attach a pair of circularly polarized phased
together to a 1" inch extendable Pole?

Thanks for helping me think through cheap ways to get more height!

Sincerely, Max
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