[TowerTalk] Boom sag on Cushcraft A4S

[Grant Saviers]

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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