[TowerTalk] rohn hbx56 & 31 foot long 432 antenna

[T A RUSSELL]

This is an old message but it points out the foolishness of
using only boomlength as a measure of antenna torque.
For the 432 MHz beam in question, it could also considered
equivalent to a 20M rotatable dipole with ZERO boom length 
and a 2 sq ft. wind load.  Would that be too much for HBX 56? 

de  Tom  N4KG
............................

On Sun, 22 Mar 1998 12:35:39 EST K7LXC <K7LXC@aol.com> writes:
>In a message dated 98-03-22 01:45:07 EST, kb0pyo@rconnect.com writes:
>
>>   I am going to be ading to my tower collection & would
>>  like some input on putting a 31 foot long 432mhz beam on a
>>  rohn hbx56. I know rohn says no boomlengths longer than 10'
>>  but this antenna only has 2 sq. feet of wind load (the
>>  antenna is very offset as far as load though, with the
>>  feedline weight in back you end up with 17 feet of boom in
>>  front & 14 feet in back with the extra windload of 14 feet
>>  of 1/2 inch heliax). I routinely see 60 mph winds here & 80
>>  + happens every couple of years, will the hbx stand up to
>>  the twist this antenna might put on it?
>
>      First of all, Yellow Medicine County is an 85 MPH windspeed 
>zone.
>
>      The HBX56 is rated at 10 sq.ft. at 70 MPH. Since you'll be using 
>the
>BX-2 section as the top section, it's better than the smaller BX-1 but 
>not as
>sturdy as the larger BX-3. 
>
>     A boom this long will generate an appreciable of torque on the 
>rotator,
>rotator shelf and then the tower itself. Over time, the rotator shelf 
>will
>crack and break. IMO it's too much antenna for the BX-2 section. 
>Better to
>lose 8 feet and use the BX-3 as your top section for torque handling. 
>You'll
>still sacrifice the rotator shelf over time but it's an improvement 
>over your
>original configuration. 
>
>    You might want to consider a Trylon Titan self-supporting tower or 
>25G
>guyed tower if you really want it to be reliable.
>
>73,  Steve  K7LXC
>
>     TOWER TECH -- professional tower supplies and services for 
>amateurs
>                                    and US Trylon distributor and Rohn 
>dealer
>
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