Ryan Niemi - AV wrote:
>
> Hi everyone,
> I've been browsing the TowerTalk reflector archives for a while,
> to gather as much info as I can before installing a small Rohn 25 at a
> hilltop site. I just received my Rohn Consumer Products catalog
> yesterday, and ran across some interesting things. Hopefully someone has
> some insight:
>
> I see Rohn usually specifies the guy radius for their towers as
> 80% of the height. But near the back of the catalog, they have some
> drawings for Rohn 25/45/55 for use with TVRO (?) dish antennas, and show
> all of them with a 50% guy radius (with 3 way guying, even), with up to a
> 6' dish at the top of the tower. The drawings are in the Mounts section,
> pages MS-62 through MS-67. Any idea what's going on here? I'm looking at
> putting up anywhere between a 40' self-supporting tower and a 60' guyed
> tower. My site will be on a small piece of leased land at the top of a
> local hill, with future lease rates depending on how much space I take up,
> so I'd certainly like to look into why Rohn shows their towers with 50%
> guy radius in some cases. My antenna load will be very light, with just a
> 17" whip at the top and a small parabolic grid at the 20' level. What are
> TVRO antennas, and why does Rohn show their towers at a 50% guy radius
> when used to support TVRO antennas? I see the Rohn drawing specifies this
> layout for a 70MPH basic wind speed, and I'm in a 75MPH zone. Would I be
> ill advised to consider setting up a 60' Rohn 25 this way? I guess I'd
> still be following the LXC directive if it's in the Rohn catalog, but
> perhaps I missed something important somewhere.. (?)
>
> Thanks,
> -Ryan
Ryan,
Makes the head swim, eh? Welcome to the world of cookbook designs, and
the notion that everything put in print is the gospel! It can be, when
we understand it, and have all the information.
The Rohn TVRO towers cite a different design spec than the standard
tower designs we use for 25G - 55G, that are designed in accordance with
EIA-RS-222-E in the latest catalogues. So, there may be some differences
involved. I don't have a copy of the spec cited for the TVRO towers, so
I have no idea what may be different. I'm sure someone does!
There's a fellow who hangs around this reflector, who goes by his e-mail
address. He sent me an e-mail a while ago when another question came up
about the vast differences between the TVRO tower designs, and the
others.
He can surely speak for himself, but I'll paraphrase what I received.
The Rohn TVRO pages are a big mistake, they are not correct, and should
not have been included in the catalogue. The sender said that this had
been verified with Rohn.
I encouraged him to let everyone else know about this (his direct
knowledge, not mine), but that didn't occur.
So, there is my contribution to unsubstantiated heresay, to add to the
fun!
Maybe, another well connected subscriber will care to verify this.
It fits right in with the incorrect antenna areas we use to load these
towers.
In your situation, I wouldn't sweat too much, it doesn't appear that you
are putting very much load on the tower. Any guys, at almost any base
spacing is better than no guys, if you get worried about it.
Doesn't sound like the antennas, you are talking about, will know the
difference between 40' and 60' when mounted on a hilltop. The dish may
care most about how much the tower moves, and that may be the real
concern.
If dish pointing accuracy is the goal (don't think the 17" whip cares),
you'll need to consider a star guy bracket to prevent excess movement.
That may be the real reason for guys, not having the tower fall over.
--
73, Kurt, K7NV
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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