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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