[TowerTalk] Adding Expanding Foam inside boom

Thu Apr 26 16:58:48 EDT 2018

I had a Hy-Gain Hy-Tower that I modified
to work better on 80. Basically extended
the top piece.
It would last a couple of New England
Winters then break.

The last time I fixed it, I epoxied a length
of Dacron Rope to one end and pulled it
tight before epoxying the other end.

Never broke again.

73, Dick, W1KSZ

On Thu, Apr 26, 2018 at 1:31 PM, Kimberly Elmore <cw_de_n5op at sbcglobal.net>
wrote:

> In a similar vein, I'm helpingto rect an antenna in a relatively
> inaccessible location and want to minimize element vibration. I have no
> intention of tryingto fill each element with foam, but I've read that
> securing a rope inside the element will prevent resonant vibration from
> occurring. If this is true, will something like "parachute cord" do the
> trick? It won't be exposed to eather, so UV deteriorartion isn't an issue.
> Kim N5OP
>
>       From: Bob Matthews <kt3rr at verizon.net>
>  To: charlie at thegallos.com
> Cc: towertalk at contesting.com; jimlux <jimlux at earthlink.net>; "Bob Shohet,
> KQ2M" <kq2m at kq2m.com>
>  Sent: Thursday, April 26, 2018 2:20 PM
>  Subject: Re: [TowerTalk] Adding Expanding Foam inside boom
>
> I used a 2 part foam many years ago on a 30 ft 10 meter Yagi boom. It made
> the boom quite rigid and strong. The materials I used were industrial
> marine grade so they would not absorb water. I’ve seen similar products on
> Amazon  https://www.amazon.com/TotalBoat-Urethane-Density-Flotation-
> Reinforcement/dp/B01AAWRYZG/ref=mp_s_a_1_1?ie=UTF8&qid=1524769730&sr=1-1
> π=AC_SX236_SY340_QL65&keywords=two+part+foam&dpPl=1&dpID=51TCGebM86L&ref=
> plSrch
> Or you can just search 2 part foam marine to see the various products
> available. I can say that the particular product I used held up very well.
> But it was so long ago I have no idea what manufacturer I used.
>
> Bob  KT3RR
>
> Sent from my iPhone
>
> > On Apr 26, 2018, at 11:42, Charles Gallo <charlie at thegallos.com> wrote:
> >
> >> On Thu, April 26, 2018 9:20 am, Bob Shohet, KQ2M wrote:
> >> I would also expect that the rate and quality of the “curing” would be
> >> impacted by the ambient temperatures and humidity levels/climate at a
> >> given location.  In much of New England the temperature can easily vary
> >> by more than 120 degrees in the course of a year – and significantly
> more
> >> in the great plains states.  And the climate can very enormously from
> the
> >> generally wet/humid East to the desert SW. This has to have an impact.
> >>
> >> 73
> >>
> >>
> >> Bob  KQ2M
> >
> > Of course there are foams (2 part) that mix on spray, and don't require
> > water vapor to cure
> >
> > That said, what is the problem you are trying to solve?  Usually foams
> are
> > used to stop vibration/change resonance frequency.  Here is the question
> > (and I don't know the answer) - how often do we see fatigue
> > cracking/failure on the BOOM of an antenna?  Not the elements - heck,
> they
> > crack on some, but I don't think I've heard of booms failing except
> during
> > extreme events like ice/wind storms.
> >
> > The foam might not give you ANY extra strength, and even you look at
> > strength/weight, I'm going to guess it'll be a net negative.  Now if you
> > know your boom has a vibration problem, we are talking another story.
> > Even then, there are probably better ways to make the boom stiffer (put
> an
> > end cap on both ends, attach a cable that runs inside the boom from end
> > cap to end cap, and come up with a way to tension the cable - aka put the
> > boom under compression, or put a metal ROD in, and put the boom under
> > tension - both will change resonance)
> >
> > The material that interests me.  I've heard that they make tube that is
> > similar to ACM sheet - basically a pair of Al tubes, with a composite in
> > between (ACM siding is polystyrene or similar)
> >
> > I'm wondering if these materials might be the way to go in new designs -
> > they are about 90% as strong, but also less than half the weight.  I
> > wonder if we could go to some of the carbon fiber/aluminum composite
> > tubes, and get MORE strength, for LESS weight (for the same size), or
> > downsize, to go SAME strength, but less area and load.. (of course at
> > greater expense)
> >
> > _______________________________________________
> >
> >
> >
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