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Re: [TowerTalk] Copy of my note to K9MI on the HDX 56

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Subject: Re: [TowerTalk] Copy of my note to K9MI on the HDX 56
From: "K8RI on Tower talk" <>
Date: Mon, 13 Mar 2006 20:00:34 -0500
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> We are turning a Explorer 14 with a boom length of 14 feet and longest
> element of 31 feet.  We are the Twin City FM Club using a  HDBX56.. 
> Have been
> doing that for 10  years!
> I dont know where you got that info on the Rohn but its not  true.    The

Quote ROHN Drawing number A-760001
NOTE:  Antenna types should be limited to those having a maximum boom length 
of 10 feet. No engineering data relating to the use of boom lengths in 
excess of 10 feet is available and the use of such boom lengths is not 
recommended.  The cover for the BX series states this 10' limitation applies 
to all BX, HBX, and HDBX towers.

ROHN does not list a HDBX 56, only the BX and HBX. The HBX is rated for 10 
sq foot and a total thrust of 200 pounds.  The tallest HDBX they list 
available is the 48'. Adding the next section makes it an HBX.  The HDBX48 
is rated for 18 sq foot and 360 pounds of thrust. However they are still 
limited to the 10 foot boom length by design.  The thrust can be applied to 
a point three feet above the apex of the tower in addition to the given wind 
pressure acting on the tower.

> windload of the tower
> is 8 sq feet which is about one med to small beam.    I  think your beam
> would work.    I dont remember the windload of  that beam but think its 
> about 8-9
> sq feet.    If you are really  concerned take the top section off and use 
> the
> tower at 48 feet and it becomes a  tank!
> Windload goes up to something like 15 sq feet!

It goes to 18 sq foot, but you still have that 10' "official" boom length. 
If the instalation has to be insurred, or engineered there are no 
engineering figures available beyong that 10'. Officialy longer than 10' 
exceeds the design specifications of the tower even if it'd handle twice 

Roger Halstead (K8RI and ARRL 40 year Life Member)
N833R - World's oldest Debonair CD-2
> -Mike
> Minneapolis
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