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From: rattmann[SMTP:rattmann@cts.com]
Sent: Thursday, August 13, 1998 5:51 AM
To: Kurt Andress
Cc: towertalk@contesting.com
Subject: Re: [TowerTalk] Guyed tower stuff
Glenn wrote:
I think the answer is: When Rohn designed these towers they probably were
looking exclusively at the "two-way" market, which in those long-ago days
meant some kind of omni-whip or simple derivative.
I seriously doubt any design engineer at Rohn ever contemplated a big
ROTATING structure with significant distributed moment like a long-boom 20m
yagi, let alone a full-size 40 or even 80m yagi. When was Rohn 45 designed?
40 years ago? I doubt there were five full-size 40m yagis in the world then.
In 1974 I had discussions with experienced user/installer Ted Gillett, W6HX,
and Frank Clement, W6KPC, then Chairman of Tri-Ex. Their advice led me to
purchase Tri-Ex T-15 stacked tower instead of Rohn. Frank indicated that
although it had smaller face-width than Rohn 45 (14", instead of 18"), the
heavy gauge legs and W-bracing made it actually superior to the Rohn in
terms of torque loads. It was designed to compete in the stacked tower
two-way market, but also with REAL ham radio in mind. In addition, the
accessory plates, top plates, guy brackets and torque bars are more
versatile and rugged than the Rohn equivalents, so it is a superior system
in my estimation, even though it is a bit harder to stand on.
I have been on the top of many tall towers with big antennas, when their
rotators were activated. All the towers wind-up a bit, but for as big as it
looks, Rohn 45 seems pretty squishy to me.
The top section of an LM-470 crankup is the equivalent of T-15, made in the
same jigs. When Frank had them designed, he made sure a small prop-pitch
motor would fit inside, anywhere you want in the section (unlike Rohn 25).
Thanks, Frank!
73, Glenn K6NA
--
Does this mean that having my 190 foot 55G towers rotate inside rotating guy
rings is going to reduce the chance for the towers twisting into a pile of
rubble in a big wind storm????? Or, does it place more concentrated angular
moment at the bottom where the rotator resists any turning?
73/Mike, N7ML
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