What I do to get accurate layout
the easy way is to use TWO tape
measures simultaneously, with
the zero ends of the tape measures
going to existing points, and the
far ends crossing over at the right
distances. IE triangulation. This
is way easier than spray painting
arcs and using temporary markers,
which is what I did before thinking
of the 2 tape measure system. You
can get cheap tape measures at
Harbor Freight, so expense is no
barrier.
Rick Karlquist N6RK
richard@karlquist.com
www.n6rk.com
www.karlquist.com
> -----Original Message-----
> From: towertalk-admin@contesting.com
> [mailto:towertalk-admin@contesting.com]On Behalf Of Mark .
> Sent: Wednesday, October 23, 2002 12:18 PM
> To: towertalk@contesting.com; n8ku@longwire.com
> Subject: Re: [Towertalk] guying tolerance
>
>
> Larry asked:
> << As I try to lay out possible guy anchor locations,I
> wonder, exactly how
> much "leeway" do I have for
> The angle with respect to each other? (nominal 120 degrees)
> The distance between anchors and tower? (nominal 80%)
> I mean, theoretically, I can get away with a steeper guying angle by
> using stronger guys and supports, right? And if the angles were
> 110-130-120 instead, what's the harm? >>
>
> As far as the angle with respect to each other, (nominal
> 120 degrees); When
> I laid out my anchor placements, I used a tape measure to
> measure both the
> distance from the base to the anchor (all three equal to
> each other, then
> measured the distance between each anchor point (again, all
> 3 equal). There
> is only one placement that satisfies all six measurements.
> If you're within
> a foot or two of the exact spot, I think it should be fine.
> You could spray
> paint arcs on the ground in the rough positions for your chosen
> anchor-to-base spacing, then trial and error with temporary
> markers on the
> arcs until all the anchor-to-anchor distances are within a
> foot or so. This
> is all assuming relatively level ground. If you have
> sloping terrain, I
> would do the geometery and vary the anchor-to-base spacing
> to keep the
> angles between the guy and ground as equal as possible.
> Comments from those
> who have done this?
>
> As far as the distance between anchors and tower (nominal
> 80%) is concerned,
> there is plenty of leeway, depending on your tower type,
> strength, and
> loading. If you are going to vary from one of the
> pre-engineered solutions
> in the Rohn catalog, I think the best practice is to
> calculate the windload
> and guying forces and make sure they are compatible with
> your guying
> hardware or have a professional engineer do this for you.
> The ARRL handbook
> gives a general guideline of 60% to 80% of tower height,
> which I think is
> still a good rule of thumb.
>
> I would try to have all base-to-anchor measurements as
> equal as possible
> (level ground), but if your tower plan is much shorter than
> the maximum for
> your tower type (190' is the max for Rohn 25, and you are
> going up 40-60 ft,
> for instance), variations of several feet shouldn't be much
> of a problem.
> I've seen short towers (60 feet of Rohn 45, which can go
> far higher) go up
> fine with two anchors out at 35 feet, and the third at 25
> feet from the
> base. The guys on the short anchor have more tension to
> have the same
> horizontal component as the other guys. It can work, as a
> custom engineered
> solution, but I don't recommend it for general practice.
>
> As far as upgrading the guy hardware, I wholly recommend
> it! My tower was
> Rohn 25, 110'. The Rohn catalog shows a pre-engineered
> solution using 3/16"
> EHS. For my installation, the greatest danger is not wind,
> but another
> nearby tree or a limb falling over on one of the guys. This
> appears to be a
> common mode of tower failure. I chose 1/4" EHS, and the
> appropriately rated
> turnbuckles, thimbles, grips, etc, for the larger size. I
> think it's
> generally accepted that modest over-engineering is good. It
> certainly is
> better than NO engineering, which is why we are all here!
>
> That ought to get the gears turning, and I'm sure there'll
> be more comments.
> Good luck!
>
> --...MARK_N1LO...--
>
>
> _________________________________________________________________
> Get faster connections?-- switch to?MSN Internet Access!
> http://resourcecenter.msn.com/access/plans/default.asp
>
> _______________________________________________
> AN Wireless Self Supporting Towers at discounted prices,
> See http://www.mscomputer.com
>
> Wireless Weather Stations now $349.95. Call Toll Free,
> 888-333-9041 for additional information.
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
|