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 Mast - Round or Square, Ali or Steel? 
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Post Mast - Round or Square, Ali or Steel?
Looking at erecting a Self-Supporting (no guy wires) 30' Mast to support a Tri-Band (6-2-70cms) V2000 Vertical and also a wire antenna (Dipole / Invereted 'L'). Question is, what should I use Round or Square, Ali or Steel Mast?

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Thu May 21, 2015 3:23 pm
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
G4NVB wrote:
Looking at erecting a Self-Supporting (no guy wires) 30' Mast to support a Tri-Band (6-2-70cms) V2000 Vertical and also a wire antenna (Dipole / Invereted 'L'). Question is, what should I use Round or Square, Ali or Steel Mast?


Round aluminium, but it will have to be a big diameter and thick wall, as even a light wire under any tension will bend it with no guy wires. (not enough to break, but enough to look bent.

I used to have two 6m lengths of 2 1/8" diameter 3/16" wall aluminium pressure pipe, it was stayed half way up, and the deflection supporting the end of a long wire was noticeable.

If it is a dipole with the centre on the pole, half the problem is gone

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Thu May 21, 2015 3:31 pm
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
Sangoma wrote:

Round aluminium, but it will have to be a big diameter and thick wall, as even a light wire under any tension will bend it with no guy wires. (not enough to break, but enough to look bent.

I used to have two 6m lengths of 2 1/8" diameter 3/16" wall aluminium pressure pipe, it was stayed half way up, and the deflection supporting the end of a long wire was noticeable.


Many thanks for the reply. The positioning of the Mast unfortunately doesn't allow for sensible guying; I'll give the thick wall tubing a try.

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Fri May 22, 2015 11:04 am
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
If you are using Ali, filling the tube with expanding foam increases the rigidity of the whole structure with a very small weight increase....


Mon Jun 01, 2015 8:40 pm
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
M6VOY wrote:
If you are using Ali, filling the tube with expanding foam increases the rigidity of the whole structure with a very small weight increase....

A handy tip, many thanks :good:

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Sun Jun 07, 2015 2:24 pm
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
I use Alloy scaffold tube, this is a picture of the mast free-standing at the end of the garden, it is about 28 feet long and supports my doublet, the doublet is 130 feet long with ends hanging down about 15 feet and supported in the middle, so there is only about 50 feet between the the Alloy pole and the Fibreglass pole supporting the middle.

Image

The ground post is made of Galvanised scaffold tube with a big block of concrete in the ground and scaffold swivel joints at the bottom, you can't see the swivels because they are in the foliage, so that I can swing the pole down if I need to.

Image

It does bend a little bit, but not that much because there isn't a lot of weight in 50 feet of wire.

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Sun Jun 07, 2015 4:22 pm
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 Mast - Round or Square, Ali or Steel? 
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Post Re: Mast - Round or Square, Ali or Steel?
G4NVB wrote:
M6VOY wrote:
If you are using Ali, filling the tube with expanding foam increases the rigidity of the whole structure with a very small weight increase....

A handy tip, many thanks :good:



Just use the right one, structural, not the one used for insulation/gap filling, it isn't suitable for a long lasting flexing installation.
The other thing to watch for is to make sure it is filled properly with no air spaces.

I don't think on thick walled tubing it would make much difference, as the forces when that collapsed would not be helped much by the foam.
It adds useful strength on thin walled tubing and fishing rods, but then you lose the flexibility that may just stop it breaking any way, but if it is just the flexing, then it works.

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Sun Jun 07, 2015 4:59 pm
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