My top loaded 80m vertical on my galvanized barn roof is made from 2 x
20' 3" irrigation pipe with a 12' diameter capacity hat. Here are some
suggestions:
You need the side guys at all times when you use a pivoting gin pole to
raise the antenna. Otherwise it is too easy to overstress the base
pivot or bottom third of the pipe as it swings on the pivot and gin
pole. If you lift with a crane or boom lift then there are no guy
constraints. If you calculate the length of the guys opposite from the
gin pole and make them 10 to 15% long and secure them, then one man can
erect the antenna to an overcenter position, tie off the gin pole guys
with some slack then adjust all guys to tightness. Obviously avoid a
windy day and it is easy to do.
I learned the side guys need to have the same base guy anchor elevation,
otherwise the geometry is wrong when lowering and raising. The baseline
from the antenna base to the guy anchor should be similar to tower guys
but can vary a bit and the raise/lower geometry will be ok. My guys are
at the middle and top which is a problem as the bottom pipe vibrates in
the wind. It is better to have unequal vertical distances between the
guys to not have resonant vibration energy coupling between sections.
I haven't seen any 40' lengths of irrigation pipe around here and the
locally available 20' x 3" wall is really thin so don't have feel for
what you need as guy points. If I was going to 60', I'd have three sets
of guys. I sawed the bell couplings off the pipes but left the part of
the coupling swaged into the Al since it is so strong. I then made an
ID adapter for between sections on a lathe, drilled and tapped it for 4
eyebolts and 4 bolts from each pipe into the adapter and used the
coupler as the guy anchor point. It's still up after 3 years and
several 60 mph wind storms on the ridge where the barn is located. I
used 1/4" black dacron rope for guys and since I run max power have some
insulators at the pipe for damp days. There is a little rope stretch
but not enough to worry about and I've experienced very long life from
this rope in the past.
If you slot a piece of pipe for a coupling sleeve, it should go on the
outside so you can clamp it with large hose clamps and/or fine thread
stainless sheet metal screws.
I wouldn't use a toilet flange as a guy point, the strength is unknown
and depending on the PVC it may not be UV resistant.
It should be a great antenna!
Grant KZ1W
Phil Chambley wrote:
> I'm looking for advice on an antenna system I'm planning on putting up this
> summer.
>
> While I'd love to have the tree height here to hang a couple of pairs of
> Bobtail Curtains, where I'm at near Helena the pines just don't get the
> water to get the height required. I've been reading back though the archives
> and gleamed some very good information on using irrigation pipe as
> verticals.
> What I am planning for 75 is a four square, last summer I cleared some trees
> and set some 4x4's in concrete for the bases. I'm planning on using 3 inch
> irrigation aluminum with one 40 foot and a 24 foot piece put together with a
> 18 inch or so sleeve of the pipe split enough to allow it to fit inside the
> other 2 pieces.
>
> For the bases on the verticals I'll take a piece of 3 inch PVC to slide over
> the aluminum and slide reducer bushings into the PVC, drill a hole through
> the bushings for the pivot point in a base built like N6RK shows on his
> website (really nice Information, thanks Rick) to lift it with another 30 or
> 40 foot piece of pipe for this purpose. The 4x4's are sticking up about 5
> feet so I can attach the verticals at this point in addition to the guys.
>
> Because I have about 10 inches of soil on top of solid sedimentary rock, I
> think I just use 1 inch round steel rod driven into the ground a couple of
> feet as guy anchors. As for the guy points on the verticals, I saw where
> someone had slipped a piece of 3 inch PVC pipe over the tubing and glued a
> plastic toilet flange on the PVC and held the PVC in place with a few
> screws, i thought that was a really good idea too. I don't know how many guy
> points 2 or 3 would be enough and where on the verticals I should place the
> guys. It will occasionally have to stand up to 70 mph winds or more but it's
> in a location where it can't hurt anything if it falls.
>
> I thought about using a 40 foot 3 inch and then a 2 inch piece on top with a
> 2 inch PVC pipe slipped over with 2 inch couplings on the PVC pipe ends and
> turn those until they just fit inside the 3 inch pipe. Not having access to
> a lathe I figured I'd just go with the 3 inch all the way.
>
> When I raise this up do I need to have the guys on the side of it too? I
> know I need to stop it when it's up but if I need to guy it so that the guy
> ropes on the side can sweep as it goes up I'll need to cut a lot more trees.
> So questions I still have: should I go 3" all the way, 3" to 2" or would 2"
> all the way work? Guy points how many and where on the verticals should they
> be mounted. Lifting the things without side guys is the possible or is it
> just plain stupid?
>
> Any tips and advice will be greatly appreciated.
>
> Thanks,
>
> Phil Chambley Jr
> KT7J
> ex KJ4NI
> _______________________________________________
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