[TowerTalk] Wind survival + load ratings... vs reality.

[Matt]

I have been extremely impressed with my JK antennas and more importantly...
the support I've received when I had questions or wanted to make changes.

Best,

Matt
K0KB

On Tue, Oct 31, 2017 at 3:41 PM, Richard Thorne <rthorne at rthorne.net> wrote:

> Jim,
>
> Good info.
>
> I don't have the #'s to back up my results as you do.
>
> I only have empirical info that coincides with your data.  I replaced an
> M2 40mLLDD with a JK SR3040 due to a bent element from a wind event.
>
> This past summer I installed a JK801, JK SR3040 and a pair of Mid-Tri's.
> Beefy is a understatement.
>
> Time will tell....
>
> Rich - N5ZC
>
>
>
>
> On 10/31/2017 1:53 PM, Jim Thomson wrote:
>
>>    Has anybody tried stuffing yagi manufactures  ele dimensions into
>> software  like  Yagi stress.....  and  or  Yagi max ????
>>
>> I have been doing just that on a bunch of them...and in several cases, Im
>> not impressed with the results.
>> And Im using the correct dimensions for exposed length tubing, and
>> correct OD and wall thickness, and correct
>> yield strength.    Im  using both the ... no spec..aka  wind tunnel
>> spec.......and also the old  C spec.
>>
>> Some of these yagis that are rated at ...  100 mph are actually only good
>> for a paltry  64 mph...and that’s  with NO ice,
>> such is the case with the M2  80m yagis.   Their  3 el  80m yagi uses C
>> specs for  wind area.  They rate it at 32 sq ft.
>> Its actually 48 square foot of projected area.   Their combo truss  +
>> LL  does nothing for ice loading, and nothing for
>> horizontal deflection.    The LL reduces some ele sag, thats it.   Both
>> YS + YM spit out 64 mph  using  no spec..and
>> both spit out  69 mph, using C spec...and that’s with NO ice.
>>
>> Toss just .25 inch of ice into the mix, and it becomes   48 mph  using no
>> spec....and    52 mph  using C spec.
>>
>> The optibeam 80m yagi doesnt fare much better.  Good for  72 mph, using C
>> spec....and less using  no spec....and that’s with NO ice.
>>
>> I also tried the JK antennas   3 el 80m yagi in YM  + YS.   Using no
>> spec, it comes in at  103 mph.  Using C spec, its good for  107 mph.
>>
>> Now that’s a helluva  big difference between  m2s  64 mph...and the JK’s
>> 103 mph.   Considering the M2 is not cheap at  $9935.95
>>
>> I have also stuffed several other yagis, like 40m, and  20, and
>> multibanders  etc  through the software.  Eye opener,  but not as bad as
>> the 80m yagis above.   I tried Mosley, Hy-gain, old telrexs,  KLM, and
>> anything else I could get exact dimensions for.
>>
>> Back in the day, ant makers could get away  quoting BS  gain and FB
>> numbers...... until software came along.    They are still  doing it,
>> but with BS wind load ratings, and max wind survival ratings.     The
>> mechanical software is readily available, so why isnt anybody holding them
>> accountable ?
>> In a lot of cases, hams are being sold a... bill of goods.
>>
>> Jim   VE7RF
>>
>>   _______________________________________________
>>
>>
>>
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