Dave
Years ago I put up 50 feet of Rohn 25 and then hung a HyGain TH3 on it. There
was no house bracket and no guy wires. The installation stood for about 10
years until the man died. I then removed the TH3 for his widow.
I know Rohn warns about bracketing and guying but lawyers are the reason for
all their understating what their product will really handle.
I would not hesitate to put up the same installation today, either. Further,
I'm planning to put up 150 feet of R55 here at my QTH and wont put any guys on
it guy it til I get up to about 60 feet. My base will be probably 3x3x3, and
I'll ultimately have 3 sets of guys on it, per Rohn's specs. Ground here, as
it was where the Rohn 25 installation was, is hard clay.
Roger aka RoGrrr
KC8HZ
> Message: 1
> Date: Sun, 1 Apr 2012 20:01:44 -0700
> From: "Dave Cook" <wa0ttn@netdave.com>
> Subject: Re: [TowerTalk] Rohn tower installation specifications
>
> It looks like the comments, both on and off the reflector, have died down
> for the evening so I'll recap what I've heard so far.
>
> 1. None of the arguments regarding the bracketing specs have convinced me so
> far. For those of you who proposed the "wet noodle" argument, I just can't
> buy that. This tower is STRONG and I think the topmost bracket is going to
> take pretty much all of the lateral strain. I didn't clarify, but the eave
> mount is actually attached to the roof, not an eave, so there's a lot of
> surface area behind it holding that bracket.
>
> 2. The only point made about the fixed base vs. a pinned base is that the
> base is intended to provide a counterweight to any sway in the tower. But
> again, with the brackets taking the stress, I don't see any purpose for the
> base other than to keep it from sinking.
>
> 3. And yes indeed, my current tower has a base of 2x2x4 feet, per the Rohn
> spec on page 25G-4 of my Rohn Consumer Catalog. In retrospect, I see the
> spec on the self-supporting tower on page 25G-2 does call for 4x4x4. But a)
> the tower has survived for 8.5 years as is, solid as a rock, and b) the
> relocation will eliminate this as an issue. Per page 25G-4, a 2x2x4 "drilled
> pier" foundation is the recommendation for bracketed towers, which is I
> suppose where I got that spec for the first installation.
>
> The last bit of info is that the Rohn spec for a bracketed tower only goes
> down to 40 feet, whereas mine will be at 35 feet. However, interpolating
> their bracketing points, which correspond to where I'll be bracketing mine,
> and with the windloading of my antenna, it should be good for 85 mph of
> windage, which would be extremely severe in my QTH. In addition to that, the
> prevailing direction of the wind is pushing the tower and antenna towards
> the house, so the worst thing I can imagine would happen in a catastrophic
> failure would be the brackets would collapse and the tower would fall into
> the house by the few inches (if any) of standoff the brackets are providing.
>
> I hope that gives a clearer picture of the situation. I think I'm going to
> be ok with putting in a 2x2x4 concrete footing, even though our soil is like
> concrete already to try to dig a hole into. But I still think that Rohn's
> bracketing specs are just way to arbitrary without some corroborating math
> to show how they came up with their numbers.
>
> Thanks again for all the feedback. I really appreciate you folks' thoughts
> on this.
>
> 73 Dave WA0TTN
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