K7LXC@aol.com wrote:
> In a message dated 5/30/01 5:20:42 PM Pacific Daylight Time, w5kp@swbell.net
> writes:
>
> > The question is: Structurally, is it a bad
> > thing to put the guys for the 74 footer at the right distance from the
> tower
> > for a 100 footer now? If I did, that would put the guy anchors at 80'
> > instead of the 56' specified, which is a pretty hefty distance change.
>
> It's all relative. The Rohn specs for guy anchor placement at 80% of
> tower height is just ONE scenario. You could have guy anchors anywhere from
> 25% or so to 200% or so of tower height and properly engineered, any of them
> would be fine.
>
> > Common sense tells me the stress on the tower
> > goes down as you move the guys further out,
>
> That's mostly right. I think there's less stress on the guys too.
>
> If you're going to have a populated tower with other yagis down the
> tower, then having shallower guy angles is very helpful to provide more room
> under them for turning side-mounted antennas.
>
> > but I suppose there's a
> > practical limit due to sag and who knows what else.
>
> That's mostly right but being a non-engineer I'll let someone else answer
> that.
>
> As was already pointed out, put the guys as high up the tower as you can
> - preferably at the top. The Rohn scenario is for commercial installations
> and not necesarily ham ones. Also check the general notes and you'll see that
> Rohn has deducted 8.0 sq.ft. for a symmetrical mount already so you can add
> the 8.0 sq.ft. back into the figure for tower capacity; i.e., if it says the
> tower will take 12 sq.ft. in the little height/loading drawing, then add the
> 8 sq.ft. so you really have a capacity of 20 sq.ft. for ham purposes.
>
> Cheers & GL, Steve K7LXC
Well, here I go again, causing trouble . . . If you look in the Rohn book at
Page HA-80
on drawing #A910214R6 it will tell you how much you can deviate from the
specified guy
radius. To save you the trouble of looking it up, Rohn clearly says plus or
minus 5
percent of the specified distance. This is not conistent with K7LXC's advice,
above,
but still I think Steve is right on here . . .
This just goes to show that everything in the Rohn book needs to be scrutinized
rather
than just "accepted" because it was written by the manufacturer. I guess this
means I
don't totally buy into the "LXC Prime Directive" but then, appartently LXC
himself
doesn't either . . . Mostly, though, the "LXC Prime Directive" is an excellent
guideline for telling you that if you are going to deviate from the "book",
check those
areas very carefully before you implement your plan . . .
This forum, for all of my past critisms, is by far the best place to test your
tower
ideas that I have ever seen. Once in awhile, you will get some goofy advice,
but it
won't stand the scrutiny of this list for long. So Steve, thanks and keep up
the great
work. I don't always totally agree with you on some of the fine points but I
ALWAYS
appreciate you being there to keep this list alive and well.
Stan
w7ni@easystreet.com
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