In a message dated 3/23/01 3:13:22 PM Pacific Standard Time, ve3tu@rac.ca
writes:
> I was wondering if any one on the reflector has any
> comments about the pros and cons of putting rope in beam
> elements. It seems that the tips are always the first part
> of the beam to self eject. I tried an elements with and
> without rope and there was a slight reduction in vibration
> with the rope (spinning an element by hand) es just
> wondering if there is an other benefit.
With conventional yagi design, the element taper was gradual. The
reasoning was that you make the elements stiff and strong. Since the element
pieces were all 'about' the same size, they would self-resonate in light
winds. Since the result was that the elements would spend a LOT of time
vibrating, they would eventually crack and break or shed pieces. The rope in
elements was a successful way to dampen this light wind vibration.
Force 12 changed this paradigm when they came out with their aggressive
taper schedule. The element starts out reasonably fat and tapers real quick.
This eliminated the element vibration and the need for rope in the elements -
two very worthwhile goals. So now the thinking is "bend like a willow" rather
than "break like an oak". It also has been shown to be useful in icing
conditions - the elements droop like crazy with an ice load but then
straighten right out with no damage when the ice melts.
Cheers, Steve K7LXC
Tower Tech
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