Details of my new 7.5m mast

As previously mentioned, yesterday I completed extending my 4m pole into a 7.5m mast. ūüôā This is all in the hope that I'll have it ready for the VHF/UHF field day next week-end. But with rain today I may not have time to finalise and test the guying system, but we'll see.

Anyway, on with the details of the setup.

The mast is now made of two sections:
– The original 4m 40mm OD aluminium tube; and
– The new 4m 44mm OD aluminium tube.
Both have a wall of 1.6mm and were sourced from Alucom here in Canberra (Fyshwick).

I also went to Bunnings and grabbed a 1m length of PVC with an OD of about 40mm and a wall of about 2mm. I've cut two 50mm lengths of this, and then cut a slit down length ways. These are then stretched over the top of one another and then over the 40mm aluminium tube. This alone is tight enough that you can actually have the 40mm tube standing inside the 44mm tube. However, once I add some beams etc I need more strength, so the PVC tubing has been pop riveted in two places to the aluminium tube.

This means there's now a nice sleeve around the 40mm tube starting 500mm from the bottom and which is about 4mm thick. This fits very nicely to act as a stopper for the 44mm base length, and further will act perfectly on the other side to rest the guy plate against (it's other key purpose). For the guy plate resting point it may not be the best as far as wear and tear long term, however I think for the amount of use it will get it should last many years. If it was going to be for a permanent setup at my QTH (rather than the field use it's intended for) I would want this to be metal.

Finally, mid way between the two overlapping sections of the tubing I have drilled a hole to accomodate a high tensile bolt. This serves three purposes:
1. Stops the sections coming apart when I'm trying to raise the mast;
2. makes the sections turn together when I rotate the mast (which for the moment, is via the strong arm method); and
3. As an extra bit of strength and security should the sleeve fail for any reason.

Anyway, so there you have it. Photos below should provide the detail of the above.

Next I'm making the guy ring. Long term I'll cut this from some steel plate, but for now as a trial of the whole thing I'm making it out of 6 ply plywood. Oh, plus I also need to make a baseplate as I don't think I'll be able to lift the mast up _with_ the beams and into the umbrella stand.

Photos:
1. Wide angle of mast free standing in umbrella stand;
2. Detail showing both sleeve and bolt;
3. Detail of sleeve;
4 and 5. Detail of bolt;
6 and 7. Detail of sleeve with 44mm section of tube slid down a bit. 

Mast_007Mast_001Mast_002Mast_003Mast_004Mast_005Mast_006

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2 thoughts on “Details of my new 7.5m mast

  1. I’m looking at something like this for permanent installation at home. My main concern has been – being made of aluminium, how rigid is it? I wasn’t planning on putting any beams at the top of mine (although that may change), but I will want a decent vhf/uhf vertical, and either/both an hf wire antenna and/or an hf & 6m vertical of some description.

  2. Heya Conrad,<div><br></div><div>To give you an indication of rigidity… Previously I used to use the 4m 40mm OD (1.6mm wall) pole for holding up both my 10el 2m beam (with a length of 4m) right at the top and at the same time my 11el 70cm beam (about 1.5m long) about 700mm below that. The pole was in an umbrella stand and tied to my bull bar. <a href="http://vk1foto.posterous.com/vhfuhf-ssb-dx-photos-17th-october-2010">Photos here</a>. (I also ran the 2m FM simplex club night with this pole and just the X-50N right at the top – and flex was a non issue.)</div> <div><br></div><div>With that setup there was almost no flex even when¬†constantly¬†rotating by hand.</div><div><br></div><div>But now it's almost twice the length, and this is why I plan to guy it just above the new 44mm OD 4m section. With that being done, I believe the flex will be very¬†minimal¬†with the beams on top. And further, for the field day this week-end I plan to mount a X-50N on the top for 2m/70cm FM work and I think this should be fine. Even with this, I still think it'll be okay. However, if it was a¬†permanent¬†setup, I'd consider adding another set of guys just below the vertical's mounting at the top.</div> <div><br></div><div>With guying, this would all definitely meet your needs I do believe – even attaching a long wire for HF. It all comes down to you need to guy it. Even a 7.5m mast made of gal pipe would need to be guyed I¬†believe – unless you used the same ODs as above and that'd weigh a bit for sure. My HF dipole at home is actually supported at one end by a 4m length of gal pipe (~25mm OD if I recall) attached to the top of a¬†clothesline¬†pole (~2m) concreted in the ground. With the tension to get the dipole relatively straight the gal pipe flexes, however previously when I just had a 2m 1/2wl vertical mounted on it there was no flex.</div> <div><br></div><div>So, I reckon it'd work for you Conrad. But just make sure you guy it. And if you don't have beams to put on it, then guying becomes very simple for you as you don't need to be able to rotate it. So you can just bolt your guy lines directly to the mast. Nice and easy.</div> <div><br></div><div>Hope that gives you some things to ponder and maybe try.¬†Alternatively, NBS Antennas (as mentioned on the VK1 Reflector recently) does have some nice pre-made masts with guying systems. You can see some photos on ebay and get an idea of price there. They will set you back a fair bit more, but maybe it'll give you the confidence you're after.</div> <div><br></div><div>Cheers,</div><div>VK1FOTO.<br><br></div>

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