In a message dated 96-12-05 12:39:20 EST, you write:
>Who out there has information or an opinion on
>the Rohn series HDBX-48. This is a 48' self
>supporting tower. I am considering putting
>up this tower at my QTH in Medina, OH (Medina County).
Hi, Gene --
First things first. Medina County is a 70 MPH wind speed zone. That's
the lowest that the TIA-222 gives so you shouldn't have any big wind problems
to worry about. BTW, the Rohn calculations are based on a wind pressure of
20 PSF, or 70.7 MPH. The tower is rated at 18 square feet at that wind
speed.
Secondly, do you have a Rohn catalog? It should be consulted during the
planning and construction phases of your project. TOWER TECH has them for
$5.00 if you need one.
The Rohn BX series of towers overall is 8 different eight foot sections
that comprise a lightweight self-supporting tower that was designed for TV
antennas. That's why they have the 10 foot boom stipulation. The tower has
little torsional resistance since the diagonal braces don't overlap; hence,
again, the 10 foot boom statement. It also has stamped steel legs and not
the nice round legs like 25G, etc. That's another strike against it in terms
of ultimate strength. Another bad feature is that the top plate (and rotator
plate) is made out of stamped tin; not the best material for larger than
average side and vertical loads on the tower. The HDBX uses the bottom 6
sections and is the heaviest and most "rugged". In their favor, BX towers
are cheap and plentiful.
> The HDBX consists of the
> I'll be putting a Cushcraft A3S or
>equivalent beam on top of it. I know this
>is not recommended by Rohn because they say
>not to use anything with a boom longer that
>10'. The A3S has a boom of 14'.
All the above said, the A3 is a pretty small load for this HDBX tower. I
wouldn't think you'd have any problems with your proposed installation.
> I might
>guy the tower, somewhat weekly with the guy
>anchors about 10' from the tower just for
>a little extra support.
Although Rohn doesn't mention anything about guys and in fact, if asked,
will probably discourage anyone from doing it, they would provide some
benefit providing that they have very little tension in them (less than 50
pounds). You don't want to tension them so that you are creating more
compressive force on those stamped steel legs.
> My main concern is
>the Rohn manual for the HDBX says to replace
>any loose rivets with bolts. WHAT? You mean
>to tell my the x-braced rivets might come out?
>I assume this means an annual trip up the tower
>to check out all the rivets, carrying a cordless
>drill and pocket full of nuts and bolts. How
>does one climb this tower with the X braces?
>
Yes, they come out and should be replaced per the Rohn suggestion. You
mean you wouldn't do an "annual inspection" anyway?
Climbing the x braces is easy. The hard part is standing on them all day
while you're working on the tower. They are real meat grinders. My feet
ache just thinking about it.
Sorry for the long winded post but wanted to give you a good perspective
of your proposed antenna support.
73, Steve K7LXC
TOWER TECH -- professional tower supplies and services for amateurs
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