[TowerTalk] Have you had success with ....

[Grant Saviers]

I think the topic "resonance of yagi elements" has a total attention in 
publications of about zero.  Then the topic, "coupled resonances of yagi 
elements" has substantially less coverage.  With a big stack it is 
interesting to watch how turning one affects all others.

IMO real understanding is beyond any rule of thumb, however I do like 
the thin wall connected to thick wall reasoning.  And building decent 
models for analysis would be exceeding difficult to get all of the 
reality captured correctly.

So if elements are buzzing or seriously vibrating then adding some 
dampening such as Telrex did for TH7s (I've had two, built to manual 
with great survival) seems like a good idea.  I also learned that a 
vertical guyed at 50% and 100% was a bad idea as the coupled resonances 
were dramatic until fatigue broke it in half.

One more comment re tip sealing.  It's very important on a SteppIR w/o 
trombones.  I really like a bit of open cell foam in the tip plus a cap 
with a hole/notch at the south edge for drainage.  Bugs kept out, water 
let out.  My 4L steppIR works FB after 7 years in rainy EWA.

Grant KZ1W

On 7/20/2019 6:46 PM, john at kk9a.com wrote:
> I used to have a 20m Hy-Gain beam in addition to my stack of homebrew 
> Yagi's.?? I used no rope and it shed element tips constantly. I am not a 
> mechanical engineer but I believe the tips break because they are made 
> from very thin walled tubing and are attached to a much stiffer swedged 
> aluminium tube instead of using a more gradual element taper.
> 
> John KK9A
> 
> 
> Richard Smith N6KT
> 
>  ??I believe that the rope in the elements, specifically the element 
> tips, is particular to the Hy-Gain yagis, at least the 20, 15, and 10 
> meter designs. I have seen a Hy-Gain yagi, a 5 element 15 meter yagi, 
> with most of its element tips broken off by regularly occurring, but not 
> huge, winds. The yagi was built without the rope in the element tips 
> that is shown in the manual for the antenna.
> I replaced the element tips in 1992, with the rope in the tips per the 
> instructions in the manual, and did not have any element tips break off 
> during the next 17 years of service at the same location.
> Just sharing my experience.
> 73, Rich, N6KT
> 
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