Towertalk
[Top] [All Lists]

Re: [TowerTalk] Mixing Rohn 20G and 25G

To: Linux Mercedes <linuxmercedes@gmail.com>
Subject: Re: [TowerTalk] Mixing Rohn 20G and 25G
From: Michael Clarson <wv2zow@gmail.com>
Date: Thu, 3 Jul 2014 13:40:12 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
I can't seem to find any 20G pricing (which makes sense, as it isn't
current production). I'm curious -- how much cheaper was 20G vs 25G?
 --Mike, WV2ZOW


On Thu, Jul 3, 2014 at 1:28 PM, Linux Mercedes <linuxmercedes@gmail.com>
wrote:

> On Wed, Jul 2, 2014 at 10:26 PM, Roger (K8RI) on TT <
> K8RI-on-TowerTalk@tm.net> wrote:
>
> > On 7/2/2014 8:38 PM, Linux Mercedes wrote:
> >
> >> Is there a significant difference between guying and bracketing a tower?
> >> I'd expect them to behave about the same, but maybe house bracketing is
> >> more rigid since guys are springy.
> >>
> >
> > There are too many variables to say for sure, but if you have ever been
> on
> > the roof of a single story home, next to a large chimney, you will be
> > amazed at how much the house roof and walls move. On a house out in the
> > open you will see the roof move a couple of inches in a 30-40 mph wind.
> >  That was a well built home.  Many brackets only guy in one axis and they
> > usually guy around 12 feet.  The wall holding the bracket should be
> > reinforced, but seldom is.  Typically, by themselves, the wall will not
> > stand against much wind until the house is completely enclosed.  I've
> seen
> > a number of them fold up when the frame and roof were completed.  There
> was
> > even a video on the net recently.. IIRC they are not insured while under
> > construction.
> >
> > Last photo on http://www.rogerhalstead.com/ham_files/Dirt_Base.htm is a
> > house btacket that attaches to a gable end consisting of 2 X 6s.
> >
> > At best the bracket only raises the base about 12 feet. Above that the
> > tower is free standing.  So you only gain what ever height above ground,
> > the bracket is located.  Brackets located on an wall not reinforced
> doesn't
> > add much stability.
>
>
> In that case, I am not too worried about guying. I don't want to bracket
> the tower (I am renting so I'm putting the tower somewhere far away from
> buildings so it can't fall on them), but I will be borrowing your dirt base
> design with some modifications.
>
>
> >
> >
> >
> >> Alternatively, I hear that for short (~100 foot or less) 25G towers,
> 1/4"
> >> EHS can be used instead of 3/16" EHS for a more rigid tower without
> putting
> >> too much weight on the legs. If flex is an issue, maybe that's the way
> to
> >> go?
> >>
> >
> > For me, EHS is way to heavy and larger is much more so.  Figure the
> weight
> > for two or three level EHS guying.
> > I replace the 3/16" guys with 1/4" wire rope (which is not as heavy as
> > 1/4" EHS) and the extra weight and tension caused the bottom two sections
> > to "bell" out between the two bolts in each leg, requiring a jack to get
> > them apart.  The stronger and heavier guys require more tension which
> > translates to more down force,
> >
>
> Wait, so 3/16" EHS is heavier than 1/4" wire rope? I do want to avoid
> permanent tower damage as I'd like to be able to take down and sell the
> tower when I'm done with it.
>
>
> >
> > I much prefer Phillystran which is far lighter and I've never, in 13
> years
> > noted any stretch problems and I've bee "up there" in winds far higher
> than
> > I should have been.  I figure 20G is about half the rating of 25G while
> > others figure 75%.  To me the lighter construction with wider spacing on
> > smaller braces along with thinner tubing for lega makes a substantial.
> >
>
>  I'd love to use Phillystran but it is incredibly expensive compared to
> 3/16" EHS.
>
>
> >
> > The legs of a 25 G by themselves are not strong.(25G=16ga, 20G=18ga)
>  They
> > depend on the braces for strength.I much prefer to err on the safe side.
>  I
> > figure, by the time you get 20G engineered to satisfy the insurance
> > company, or codes if applicable, you could have purchased and installed a
> > 45G.
> >
>
> That makes a lot of sense. The leg braces on 20G are thinner, too. If I use
> it at all, it'll be at the very top of the tower.
>
>
> >
> > Had I known I wouldn't be able to continuing to climb through my 70s, I'd
> > have found a way to install a heavy duty 100' crank up instead of the
> 100'
> > 45G.  To me, going up needs to be safe, with a good safety margin.  I use
> > guy brackets and do not tie guys to tower legs so the whole tower
> receives
> > the sideways/lateral force, not just one leg. If you do not use a pier
> pin
> > base, wing transfers a lateral force to the back side (side away from
> wind)
> >  and an upward force to the front side (side on which the wind impinges).
>
>
> Fortunately I'm young and stupid so I'm not too worried about tower
> climbing. I do need to pick up a guy bracket for the middle bay; I was
> debating making my own since Rohn wants something outrageous for theirs,
> but I'll probably pick up one from Norm's Fab as they're a bit cheaper and
> I don't have to spend the time designing it myself. Fortunately, the tower
> I was given came with a flat top that has loops for guy wires built into
> it.
>
>
> >
> >
> >  Although if leg weight loading is a concern, I guess I should work out
> >> how much downforce a 20G section can support, since it'll be less than
> 25G.
> >>
> >>
> > 18Ga Vs 16ga  (3,900# for 18ga 20G.  I don't have a figure for 25G)
> >
>
> Neat. 20G will collapse before the 3/16" EHS guys you'd use on it will
> break. I guess that is why it's not recommended for much!
>
>
> >
> > 73
> >
> > Roger (K8RI)
> >
> >
> >
> >  --Nathan
> >>
> >> On 07/01/2014 10:32 PM, Wayne Kline wrote:
> >>
> >>> Two levels of guy is what my concern would be. I am in as now and be
> >>> home in PA next week.
> >>> I have a library or Rohn catalogs and in the older ones I have the full
> >>> spec on r 25 -G.
> >>> But if my gray matter serves me well  R 25- Gg is not suitable for
> >>> guying let alone two levels .
> >>> And this was the old spec. So with out a house bracket your walking on
> >>> thin ice.
> >>>
> >>> YMMV
> >>>
> >>> Wayne W3EA
> >>>
> >>> Sent from my iPad
> >>>
> >>> On Jul 1, 2014, at 6:24 PM, "Linux Mercedes" <linuxmercedes@gmail.com>
> >>> wrote:
> >>>
> >>>  Wayne,
> >>>>
> >>>> I'll primarily be using it for wireless internet. Unfortunately, the
> >>>> tech at the WISP I spoke to was pretty vague about the wind load of
> the
> >>>> antenna they'll be using, but he assured me it would be 'minimal' and
> >>>> didn't think it would be that big of a concern.
> >>>>
> >>>> I won't be house bracketing this install, but it will be guyed at two
> >>>> levels (what Rohn recommends for 50' of 25G).
> >>>>
> >>>> --Nathan
> >>>>
> >>>> On 07/01/2014 09:59 AM, Wayne Kline wrote:
> >>>>
> >>>>> I also have experience with 20-G and 25-G towers... @ my station my
> >>>>> 2mter/450 MHZ  and one 6 meter beam
> >>>>>   5 element 14' boom  are on at 36ft. an consist of  3 sections of
> >>>>> 20-G and a top of 25-G  AG3 ?   it's house bracketed @ 18 ft.
> >>>>> Been in place for 24 years  BUT  extremely light wind load.
> >>>>>
> >>>>> IMHO  @ HF  a C-3. TA33  or A3 would be the BIGGEST  .
> >>>>>
> >>>>> So my question to you is WHAT are you planning to adorn the tower
> with
> >>>>> ?
> >>>>>
> >>>>> Wayne W3EA   . .
> >>>>>
> >>>>>
> >>>>>  Date: Tue, 1 Jul 2014 07:42:14 -0500
> >>>>>> From: kkbroadcastengineering@gmail.com
> >>>>>> CC: towertalk@contesting.com
> >>>>>> Subject: Re: [TowerTalk] Mixing Rohn 20G and 25G
> >>>>>>
> >>>>>> Nathan,
> >>>>>>
> >>>>>> I would caution you to not mix the sections nor even use the 20 for
> >>>>>> anything more than VERY light duty use.
> >>>>>>
> >>>>>> With that said...  Back in my younger days when I did a lot of tower
> >>>>>> work
> >>>>>> for CB and Ham operators, there were a number of mixed 20/25 towers
> >>>>>> supporting large CB antennas and they stayed up many years.  I do
> >>>>>> recall
> >>>>>> working on one where the 20 top section physically broke during a
> wind
> >>>>>> storm.
> >>>>>>
> >>>>>> Climbing a mixed 20/25 tower is a real pain as the steps are
> different
> >>>>>> distances apart.
> >>>>>>
> >>>>>> Good luck,
> >>>>>>
> >>>>>> Kevin C. Kidd, CSRE/AMD
> >>>>>> AM Ground Systems Company  -  WD4RAT
> >>>>>> kkidd@kkbc.com  --  866-22-RADIO -- 866-227-2346
> >>>>>> www.amgroundsystems.com
> >>>>>>
> >>>>>>
> >>>>>> On Mon, Jun 30, 2014 at 7:42 PM, Linux Mercedes <
> >>>>>> linuxmercedes@gmail.com>
> >>>>>> wrote:
> >>>>>>
> >>>>>>  Hello,
> >>>>>>>
> >>>>>>> Whilst moving tower sections from the shed to the shop so I could
> >>>>>>> clean
> >>>>>>> them up and make a couple of fixes before putting up my tower, I
> >>>>>>> noticed
> >>>>>>> that some of them seemed lighter than others. Turns out I've got a
> >>>>>>> mix of
> >>>>>>> 20G and 25G sections.
> >>>>>>>
> >>>>>>> What are your thoughts on putting up, say, 30 or 40 feet of 25G and
> >>>>>>> then
> >>>>>>> another 20 or 10 feet of 20G? I'd like to use the best sections I
> >>>>>>> have on
> >>>>>>> the tower, but if mixing is a no, then I'll fix up some of the
> other
> >>>>>>> sections I have and build a homogeneous tower.
> >>>>>>>
> >>>>>>> Thanks,
> >>>>>>> Nathan
> >>>>>>> _______________________________________________
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> _______________________________________________
> >>>>>>> TowerTalk mailing list
> >>>>>>> TowerTalk@contesting.com
> >>>>>>> http://lists.contesting.com/mailman/listinfo/towertalk
> >>>>>>>
> >>>>>>>  _______________________________________________
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>> _______________________________________________
> >>>>>> TowerTalk mailing list
> >>>>>> TowerTalk@contesting.com
> >>>>>> http://lists.contesting.com/mailman/listinfo/towertalk
> >>>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>>
> >>>>>
> >>>>>
> >>>>> _______________________________________________
> >>>>> TowerTalk mailing list
> >>>>> TowerTalk@contesting.com
> >>>>> http://lists.contesting.com/mailman/listinfo/towertalk
> >>>>>
> >>>>>  _______________________________________________
> >>>>
> >>>>
> >>>>
> >>>> _______________________________________________
> >>>> TowerTalk mailing list
> >>>> TowerTalk@contesting.com
> >>>> http://lists.contesting.com/mailman/listinfo/towertalk
> >>>>
> >>> _______________________________________________
> >>
> >>
> >>
> >> _______________________________________________
> >> TowerTalk mailing list
> >> TowerTalk@contesting.com
> >> http://lists.contesting.com/mailman/listinfo/towertalk
> >>
> >
> >
> > _______________________________________________
> >
> >
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk

<Prev in Thread] Current Thread [Next in Thread>