[TowerTalk] High VSWR

[Robert Harmon]

I have been thinking about getting a big Steppir DB36.  You guys are scaring me off.   hihi

Bob
K6UJ





> On Sep 1, 2019, at 3:10 PM, jimlux <jimlux at earthlink.net> wrote:
> 
> On 9/1/19 11:41 AM, Doug Ronald wrote:
>> I would like to talk to you about that vane idea when I get further along on
>> the repair of this LP. Those back 4 elements are really heavy, so placing
>> the boom-to-mast mounting plate in the physical center of the boom would
>> have required massive counter weights on the high-frequency end of the boom.
>> There are already two counter weights there now with about 240 pounds weight
>> total.
>> The wind torque on this antenna is so much that I have to remove the drive
>> chain from the rotor in a storm to prevent breaking the shear pin in the
>> rotor.
>> If the vane idea will neutralize the boom's torque, what about the 104 foot
>> long back elements? In a steady wind, how will the antenna orient itself if
>> free to rotate 360 degrees? Of course now in a steady wind, the butt end
>> always faces the wind direction.
>> Doug, W6DSR
> 
> 
> I would also wonder about the elements flexing in the wind load. Both from an oscillation standpoint (what's the first mode frequency?) and from a scenario where the element bends, which changes the "projected area" relative to the wind, so the drag changes, etc.
> 
> Of course, in some cases, there is "previous installation experience" to look at - if there aren't any design changes, and they've got live experience with the antenna not failing in a wind of X mi/hr.
> 
> But the whole resonant excitation thing is a challenge to model properly, especially if the element is tapered (since the stiffness changes with position along the element, as does the aeolian excitation frequency).
> 
> 
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