Without doing the numbers, I agree with Mal. My 97' Rohn 25 has 2 x C3Es
on it, at 97 and 69 feet, and a F12 240S 6 feet above the top C-3. That
has to be less wind area than you are proposing, and when I thought about
adding a third C-3E, I did do the numbers, and discovered I would be well
over the tower's rating.
You probably don't need to worry too much about resonances, since your
antennas will be above the guys. Until I put in the second C-3 inside the
top guy set, I had steel top guys, and had no issues, though I did have
21-foot Joslyn fiberglass power pole insulators on the top guys to get the
steel a little way away from the antennas. A consideration with
Phillystran is that it stretches about twice as much as EHS steel for a
given tension, which arguably could derate the tower a bit more compared to
using steel guys, particularly if you have an embedded base section rather
than a pier pin.
In any case, if you use EHS, I suggest you put insulators at the top end of
each guy set, so that you can shunt feed the tower if you want to, for 80
and 160.
73, Pete N4ZR
At 03:45 PM 6/11/2008, N7mal wrote:
>I have put up a lot of rohn 25 because I have a lot of faith in it. I have
>found the specs on rohn 35 are under rated. Rohn 25 will handle a lot. BUT
>I'm not even 'gutsy' enough to try what you are going to try. I think you're
>fine with weight and 'regular' wind loading. If you get a lot of gusting
>winds you might and probably will be in trouble. You will also be in trouble
>with ice. Your best bet is to move up to Rohn 45.
>Just my -2 cents worth.
>73
>
>
>MAL
>N7MAL
>BULLHEAD CITY, AZ
>http://www.n7mal.com
>Everyone in the world is
>entitled to be burdened
>by my opinion
>
>
>----- Original Message -----
>From: Jwpjj@aol.com
>To: towertalk@contesting.com
>Sent: Wednesday, June 11, 2008 18:42
>Subject: Re: [TowerTalk] Guying Material and resonance
>
>
>I am getting ready to install 90' of Rohn 25, base section is all
>done,concrete etc and so are the guying stancheons that are set in concrete
>as well. I
>have the first 10' up and hopefully in a few weeks or so will be ready for
>the rest of the installation. My question is what is preferred, steel guying
>cable or Phillystran cable. One of my concerns ( maybe it should not be) if
>I
>use steel guying installation, should I be concerned about resonance based
>on
>the lengths of guying cable. The tower will have a 4 el steppir at approx
>98',
> below that there will be a 3 element 40 meter monobander, prosistel rotator
>and fed with LMR400. Will I need to break up the guys? It seems like it
>would
>be a lot of work if I had too or should I just go for the Phillystran and
>don't be concerned. This is my first guyed tower as I have always have had
>crank ups. I have seen a lot of pictures that have been on this forum and
>was
>wondering what most everyone else uses for guying their towers. The guying
>lengths will be as per Rohn specs, 80% of total height to calculate guys
>lengths.
>
>John, ND1X
>
>
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>
>
>
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