Yes, was just on their site yesterday and bought from them earlier this
summer.
https://jkantennas.com/
73,
Mike ND9G
On Wed, Nov 1, 2017 at 1:10 PM, Herbert Schoenbohm <
herbert.schoenbohm@gmail.com> wrote:
> JK Antennas come up "site not available" on all my attempts to reach them.
> Are they still in business? All my HY-Gain LJ 5 element beams for 20-10
> survived Cat 5 Hurricane Maria with it's 179 MPH sustained winds but they
> were all on the ground held down with large wooden pegs. ☺ MY 4 element
> CUBEX QUAD up on the tower with the least W/L looks like scrambled eggs. As
> the man in the movie JAWS said "We need to get a bigger boat."
>
> Herb, KV4FZ
>
>
>
>
> On 11/1/2017 12:17 PM, Jim Thomson wrote:
>
>> Date: Tue, 31 Oct 2017 23:58:52 -0700
>> From: Kurt Andress <andresskurt@gmail.com>
>> To: towertalk@contesting.com, jim.thom@telus.net
>> Subject: [TowerTalk] Wind survival + load ratings... vs, reality.
>>
>>
>> Hi Jim,you wrote...
>>
>> -----Original Message-----
>> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
>> Jim Thomson
>> Sent: Tuesday, October 31, 2017 1:53 PM
>> To:towertalk@contesting.com
>> Subject: [TowerTalk] Wind survival + load ratings... vs reality.
>>
>> 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
>>
>>
>> <W3JK, who uses my software, put me onto this post...
>> <Now you guys are catching up with me, from the work I did in the 1980's
>> to spend about 8 years creating YagiStress, and getting it verified by one
>> of my P.E. colleagues with $18k software, Yagistress is within ~ 1% (or
>> rounding errors) with the pro finite <element linear analyzing engines.
>>
>> <What you're seeing Jim is what I have seen for around 30 years, and I
>> have made comments on this reflector many times about that, but they were
>> greatly ignored! I got run off this platform by too many other jungle
>> knowledge experts that want to rule the <roost with their ever present
>> emperical expertise! So, that's why I no longer devote much of my time to
>> this venue....it is frought with way more "Jungle Knowledge" than
>> engineering expertise!
>>
>> <Have fun out there imagining how you wish it would be, but not how it is!
>>
>> <73, Kurt Andress, K7NV, author of the YagiStress software...and tower
>> service provider
>>
>> <P.S. You should simply throw away the EIA/TIA 222-C spec, it is now
>> about 28 years old and does no longer apply!
>>
>>
>> ## Points well taken. What I still dont get is.... the effects of the
>> element tips bending. I call that...shedding wind. I dont believe the
>> software factors that effect into the equation. I have seen F12 els,
>> where the tips and inboard sections from the tips, are bent straight back,
>> and the even more inboard sections still dont break ! IE: when the ends
>> bend way back, the wind is now hitting them at a shallow angle..and less
>> force applied to the ele ends. The cross flow principle, so to speak.
>> Having said all that, when m2 is good for 64 mph..and the JK is good for
>> 103 mph, thats a HUGE disparity..... yet both are rated for...100 mph. In
>> actuality, the actual breaking mph is probably 20 % higher than what the
>> software spits out.
>>
>> ## M2, F12, Mosely, Hygain, STILL use the outdated 222-C spec. You
>> have to add exactly 50% to their square footage, to get the real projected
>> areas. To find out what their yagis are really rated at, you have to take
>> their eles, typ the REF..and stuff the dimensions into either YS or
>> YM.... then judge for yourself. I dont mess with the C spec, nor the
>> 222-F spec, nor the UBC-97 – exposure B/C/D spec. I use the... No spec,
>> aka wind tunnel...and so do many others.
>> Heres what YM spits out for the m2 80m REF using various standards.
>>
>> No wind spec - 64.802 mph
>> EIA-222-C spec - 69.759 mph
>> EIA-222-F spec @ 100 ft - 50.397 mph
>> UBC- 97 Exposure B @ 100 ft - 60.492 mph
>> UBC- 97 Exposure C @ 100 ft - 50.093 mph
>> UBC- 97 Exposure D @ 100 ft - 45.549 mph
>>
>> Use a 200’ tower instead of a 100 ft tower....and they all drop aprx 5
>> mph.
>>
>> IMO, measure the speed at the top of your mast... using a wireless,
>> accurate, peak reading, wind speed indicator. Forget the fastest
>> mile..and 3 sec gust bs. I want the actual peak wind speed, and if a gust
>> comes along, its the gust speed that I use. Its also the gusts that break
>> stuff. The sustained wind speed is nice to know.... but its the higher
>> speed gusts that I want to know about. I dont want a wind speed indicator
>> on the side of a tower either, nor the side of a mast. Depending upon
>> wind direction, the tower ..or mast could impede airflow, and result in a
>> lower reading. Taking the wind speed from the 6 oclock news is a wasted
>> effort. Done on the far side of town, at a much lower elevation, typ 33
>> feet.
>>
>> I would suggest to JK ants, who actually builds the...real deal, to
>> tabulate both his ants, and all his competitors using YS + YM....then
>> post the results on his website... for all prospective clients to see for
>> themselves. Then if the competitors whine + complain... too bad so sad,
>> either put up...or shut up. Since his competitors use the C spec, I would
>> suggest posting both the C spec..and also the NO spec...aka wind tunnel
>> results. Then at least joe ham can compare yagis...using the same spec.
>> M2 Stating their 80m yagi is 32 sq ft and good for 100 mph, when software
>> sez its 48 sq ft and good for 64 mph is nothing short of reprehensible.
>> Then folks can use the correct info to make an informed decision as to
>> actual tower type required, and also rotational torque required....and if a
>> given yagi meets their site dependent WX requirements for expected max
>> windspeed and gusts..and any ice loading, or heavy wet snow. While we
>> are on a rant, lets minimize ant torque. Easily done with either a small
>> counterweight and or a Torque compensation plate.
>>
>> If one of these large 200-500 lb yagis ever cut loose... and came
>> crashing down....and sliced a phillystran guy wire, or a solid fiberglass
>> guy wire..... the entire tower could easily come down. Neither philly
>> nor solid fiberglass has any shear strength.... only good tensile
>> strength. Thats a safety issue imo.
>>
>> Id be right pissed if my competitors were spewing BS numbers. And no, a
>> cross bar mounted above either an element or boom, with dual truss lines on
>> either side, doesnt increase the max wind speed. Heck it doesnt even
>> reduce the horz deflection.
>>
>> end of rant.
>>
>> Jim VE7RF
>>
>>
>>
>>
>>
>>
>> _______________________________________________
>>
>>
>>
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