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, firstname.lastname@example.org 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
> The HBX56 is rated at 10 sq.ft. at 70 MPH. Since you'll be using
>BX-2 section as the top section, it's better than the smaller BX-1 but
>sturdy as the larger BX-3.
> A boom this long will generate an appreciable of torque on the
>rotator shelf and then the tower itself. Over time, the rotator shelf
>crack and break. IMO it's too much antenna for the BX-2 section.
>lose 8 feet and use the BX-3 as your top section for torque handling.
>still sacrifice the rotator shelf over time but it's an improvement
> You might want to consider a Trylon Titan self-supporting tower or
>guyed tower if you really want it to be reliable.
>73, Steve K7LXC
> TOWER TECH -- professional tower supplies and services for
> and US Trylon distributor and Rohn
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