[TowerTalk] Need recommendations for a 40-10m. Yagi
jim.thom at telus.net
Sun May 6 12:44:03 EDT 2018
Date: Sat, 5 May 2018 17:34:33 +0000 (UTC)
From: Timothy Coker <n6win at yahoo.com>
To: <kstover at ac0h.net>, <rlvz at aol.com>, <towertalk at contesting.com>
Subject: Re: [TowerTalk] Need recommendations for a 40-10m. Yagi
<I could be wrong... but I believe your not looking at an apples to apples windload between the two.
<I?m seeing 16.5 sq ft for the JK Mid Tri w/40m and 17.8 sq ft for the Optibeam. Notice how Optibeam only lists one rating where as JK lists three which can confuse things in that Ken is giving more information.
<As for the aluminum being the same... way smarter guys here than me. I?ve been curious of late if that?s really the case... I?ve been reading about some boom failures at other stations of late and there are some very adamant hams talking about the quality <differences in aluminum used. Could just be angry folks, I?m no mechanical expert.
<If the original op is saying he?s mainly into the contests he?s probably going to want to keep his contest yagi?s as clear of his WARCs as possible in order to avoid possible interaction so that he obtains better performance during the contests.
<I first started out trying to do everything I could on 10 feet of mast sticking out of Rohn 25G. Who knows what was happening with a TH7DX at the thrust bearing, an A3WS/30m 5? above and a XM240 driven element at 10? above. Oh and toss in an 80m <inverted V a foot below it all! :)
<Going forward I?ll put my WARCs on separate structures or as temporary wires as needed. Just less for me to worry about when people aren?t returning to my CQ?s.
<That?s me though. Try to make it so the scores aren?t so much limited by hardware and more by me.
<Tim / N6WIN.
## The JK Mid tri with 40m IS 24.75 sq ft of projected area. Projected area means length X width for each ele. Then total up all the areas of all the elements. The 16.5 sq ft for the mid tri with 40m is the old C spec.... no longer used.
The old C spec took the projected area.. then multiplied it by .666 to get... effective area. This is what F12, hy gain, etc used...and plenty of ant makers still use the old C spec. To get from old C spec ratings.. back to projected area, just multiply by 1.5. EG: 10 sq ft projected = 6.666 sq ft using c spec. 6.666 X 1.5 = 10 sq ft. For all you folks using yagis with the old C spec ratings.... multiply by 1.5 to get reality.
## 16.5 X 1.5 = 24.75 sq ft projected... which is what the mid tri + 40m actually is.
## I would not even mess with the F or G spec, too convoluted and requires the actual installed height to be factored in, plus a ton of other variables, including wind exposure etc. IE, buried in a forest of trees, in the middle of a wheat field, on a ridge, or next to salt water, etc.
## When the projected area is run through the mech software, to calculate max wind rating, like when using DX engineerings ...Yagi mechanical, it will spit out max wind survival for any spec you want, including F, G, C.... and also UBC-97..with its associated A, B, C, D.. wind exposure. It will also spit out.... No spec. No spec is what you get when using a wind tunnel... which is good enough for myself... and is a bit more stringent vs the old C spec. If you installed a wind speed indicator at the top of your mast, you will get the same results as using a wind tunnel. Yagi mechanical will also spit out the ele deflection at any wind speed you want, from 0 up to max wind survival. Ken uses NO spec to calculate the max wind survival ratings of his yagis. Its very conservative imo. Also when the eles deflect, the tips shed wind, aka reducing the loading. That alone will add an additional safety buffer on top of what the NO spec spits out. 40M eles will deflect more than a 20M ele, and unload even more. The JK 40M els dont sag, and dont require a truss.
## Several folks have had severe issues with the way optibeam splices their square boom sections together. I dont like their boom to mast assys, it uses 2 x muffler clamps for the mast. Nobody uses muffler clamps for anything these days, esp the types with sheet metal saddles, as depicted. https://www.dxengineering.com/parts/dbo-ob12-4w-p JKs version wont budge or slip on any mast. Optibeam uses METRIC tubing sizes for the elements..and also the square and also their round booms.
Unlike 6063-T832, 39 ksi yield strength...... or 6061-T6, which uses 40 ksi yield strength..and both using standard tubing sizes and wall thickness, METRIC tubing does not telescope with a snug fit. They make a sloppy fit and have to be either shimmed, or swaged.... pita. The deal breaker for myself is that METRIC tubing is a bitch to find in Both Canada..and the USA. A buddy finally found one source for metric tubing in the usa....and it was special order, and expensive. That may have changed. So even if you can find replacement METRIC tubing in the usa, next up you will have to get the ends carefully swaged. Any swaging process has to be done dead one. Too little or too much, and you are in trouble..esp if too much.
## If you are hell bent for the optibeam, even if you ordered it asap, it wont ship from Germany until August 13, 2018. $3378.00 vs $2695.00 for the JK. The $683.00 difference is not exactly chump change either..and better put towards the JK-801. The optibeam uses an included 2:1 balun. That would kill it for me right then and there. The JK uses a simple 1:1 CM choke for the 20-15-10m portion.... and a 2nd 1:1 simple CM choke for the 40m portion.
## JK WELDS the ends of their 40 loading coils, made from solid .25 Al rod, comes in large rolls. Zero resistance connections. I would install the jk mid tri with 40m just a few inches above the top of the tower, and the 801 towards top of mast..then call it a day.
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