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Re: [TowerTalk] Boom sag on Cushcraft A4S

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Boom sag on Cushcraft A4S
From: Kevin <kstover@ac0h.net>
Date: Thu, 6 Oct 2016 19:39:08 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
My father has had an A4S up for nearly 25 years sans a boom truss.

We live in Iowa. We have real winter.

We haven't seen the kind of damage Grant is talking about. When it comes down for bi-annual maintenance we put a new coat of clear Krylon on the center insulator. I do agree with replacing the DE center tube with solid fiber glass rod. I built that beam in my fathers driveway and installed it before I ever had a license. The beam outlasted a roof tower of questionable manufacture and is now happy on 39' of Rohn 25 tower and Yaesu G-800 installed on his flat garage roof.


On 10/6/2016 4:57 PM, Grant Saviers wrote:
The boom is not particularly heavy duty IMO (I have 2x A4S). If icing is likely a Phillystran truss would be a sensible addition. Also it is quite easy to deform the boom with the element clamps and since mine are used in Field Days, taken apart and back together yearly, I have internally sleeved the boom at each element attach point. A few sleeves required significant "urging" to go in and copious amounts of Penetrox since they were a bit deformed.

Same for the u-bolt holes in the elements, an overly enthusiastic FD assembler flattened the element. Simple sleeving and new holes solved that problem after sawing out the center.

The fiberglass driven element center insulator rots in a few years in the sun, so a couple of coats of clear acrylic spray are longevity inducing. I replaced mine with solid FG rod rather than the factory FG tube.

Another weak spot is the element to boom clamps can splay out and loosen, yielding tilted elements. I made mine square in a vise and used long SS 6-32 machine screws and nylock nuts side to side to keep the ears from bending outward. Not much space with the u-bolts but they do fit.

Amazingly, even in dry CA, I had a boom fill up with water - duh. Quite a surprise when I loosened the boom to mast bolts. So notch the end caps on the elements and boom at the lowest point. Large enough so water gets out and small enough so hornets don't get in.

Otherwise it is a good antenna, no trap problems at 1kw, decent performance for boom length, etc. Mine are original CC, I can't speak to "value engineering improvements" by MFJ.

Measure three times all dimensions before "up the tower". It is sensitive and nobody on the FD team ever got it right first try. (even before the 807's). Below 15' or so height swr measurements are useless.

Grant KZ1W


On 10/6/2016 14:25 PM, Bill DeVore wrote:
I’m getting ready to put up my first beam. I’ve noticed the ends of the boom on the A4S sag about 3-5 inches below the center point. Would making a truss out of a non stretching material such as phillystran be worth the effort or am I just being anal about it? The boom is not bent.

Bill - W3PNM
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R. Kevin Stover
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ARRL
FISTS #11993
SKCC #215
NAQCC #3441


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