HDBX help

[K7LXC@aol.com]

In a message dated 96-12-07 16:05:56 EST, you write:

>I was wondering if you had any ideas on how a Rohn HDBX-40 could be extended
>in
>height to maybe 48ft? I would like to use mine as a top loaded vertical and
a
>little extra height would be welcome. It seems that Rohn used to sell
>straight
>sections, but no more.

Hi, Chuck --

    The Rohn BX series consists of eight 8-foot sections.  I'm not sure what
an HDBX40 is since I thought all they marketed was the HDBX 48.  You should
have the Rohn catalog.  Then you could measure the sections and see which
ones you have.  Then all you have to do is get the next smallest section and
you'll be up to 48 feet.  The total wind loading depends on which sections
you're using.  

HDBX48    sections 8 thru 3   18 sq. ft. wind load capacity
HBX56      sections 8 thru 2    10 sq. ft.
BX64        sections 8 thru 1     6 sq. ft.

    TOWER TECH has the Rohn catalogs for $5.00.

     You may be able to find old straight sections around.  BX towers are
very plentiful and if you put the word out, I'll guarantee that some will
drop in your lap.  Also, the BX is made is Canada under the Delhi name.  They
make all of the old straight sections that Rohn quit making years ago.
 Another thing you can do (I've done this many times myself) if to get some
used sections and cut off the tapered bit.  Drill some new bolt holes and
you've got yourself a serviceable 7 foot or so straight section.  Talk about
quick and dirty.

> In addition, I'm considering putting up a C4SXL to get
>some 40m gain and it will have a Cuchcraft 17B2 2m yagi abt 6-8 feet above
>it,
>so I don't want to give up too much wind load capacity. BTW, what is
>considered
>to be a "large" twisting moment? 

    The twisting moment is limited to the 10 foot boom that they specify at
20 PSF wind pressure (70 MPH).  If you've got an HDBX, obviously you have
more capacity than that.  The boom length limit is mostly for BX towers using
the #1 (smallest) section.  It still has its torsional limits though.

>I'm going to get one of Rohn's books from you
>anyway, but was wondering if they specified any figure. I currently have an
>Explorer-14 (18 ft boom) up for a number of years with no problems, but
would
>like to know. I enjoyed your "one tower station" writeup - I would have
liked
>to get a tower in the 60ft range, but I didn't think I could get that past
>the neighbors and the XYL wouldn't like the guy wires. The HDBX seemed to be
>the the best compromise, I just wish I had gotten the 48 footer (since I
>haven't heard anything from the neighbors).

    Since the tower load will be decreased by going up one more section, I
don't know if it would be worth it for another 8 feet.  You'd have to go up
another 20-30 feet to notice any difference IMO.  

73,  Steve  K7LXC

   TOWER TECH -- professional tower supplies and services for amateurs



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