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
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441
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