The 2x2x4 chunk of concrete is called ballast.
Similar to the keel of a sailboat...helps to keep it upright.
On Sun, Apr 1, 2012 at 2:24 PM, Dave Cook <wa0ttn@netdave.com> wrote:
> Hi guys, I'm in the process of relocating my 35' freestanding Rohn 25G
> tower
> after 8.5 years on the air. I figured this time I'll bracket it to the
> house, which is what I should have done in the first place. But I've run
> across a few problems with the Rohn specifications:
>
>
>
> 1. The tower will be bracketed to the house mid-way up and also near
> the top of the tower with an eave bracket. The specifications for the
> brackets "must support a minimum horizontal force of 815 pounds". I can't
> find any calculations for how they came up with this number. And it seems
> very excessive for a modest 35 foot tower bracketed in two places.
>
> 2. The specs also state that the base must be a "fixed base", rather
> than a pinned base. Again, in this case I don't understand why a pinned
> base
> wouldn't be sufficient for a well-bracketed tower. Why would the base
> experience any lateral loading?
>
> 3. The specs also state that the base has to be the same 2x2x4 feet
> of
> concrete that was spec'ed for self-supporting and guyed towers. In this
> case
> I can understand somewhat having a solid chunk of concrete for the thing to
> rest on, but the entire weight of the tower and antenna will be, by my
> calculations just a little over 200 lbs. It doesn't seem to me that it
> needs
> a 2000 lb chunk of concrete to keep that from sinking into the soil.
>
>
>
> So in short, I'm just wondering if Rohn is simply CYA'ing themselves, or
> are
> these specs really to be taken literally?
>
>
>
> Thanks and 73,
>
> -- Dave WA0TTN
>
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