Saturday, May 20, 2017

Rebuilding the Homebrew Hexbeam Antenna

So Clint's M0FHN Hexbeam antenna has arrived and at last I had some time to inspect it properly. It's very well built and interestingly he used an aluminium tube for a centre post, using extra coax as the ground. Because of this, the antenna is quite heavy, 15/16kg about 34lbs and that's not including the rotator, I'm not sure with the weight it will go on my new tilt over mast, it may be too heavy.

So what I thought I do is keep the aluminium centre post all in tact as it already has the element connected and is well weatherproofed, keep the reflector elements as well, store them all away. 
I'll remove the base plate, take the glass fibre spacer poles and the support cables which are all roughly measured out and I can adjust if needs be, use those in conjunction with a new lighter centre post made out of some thick fibre glass pole I had left over from making the 17 meter moxon.

I still have some 14 gauge wire left over from my Cobweb days and I'll use that for the new elements. This will give me valuable experience in building a Hexbeam and apart from the glass fibre spacer poles (which can easily be replaced) and I still have another spare Hex antenna.

I started on the centre pole yesterday and have been following K4KIO 's site on building the G3TXQ broadband hex, but adapting where I need to. The measurements for the centre post are the same and I have now drilled and fitted the wire terminals bolts. I've also fitted the top cap and a large bolt to take all the support cords.
The centre post
The wire terminals bolts are a little bit tricky to fit, but using a long piece of wire folded over attached to the bolt, you can fit them threw each drilled hole. These terminals will all need to be waterproofed with either hot glue or waterproof liquid tape. It's essential that everything is thoroughly protected from the weather or else the SWR can be effected.
The PVC cap is off another project and together with a bit of waterproof tape and glue it is wedged on to the top of the fibre glass pole. Again I will make sure it's tightly fitted by pouring some more hot glue underneath it. This has to be a good fit as it will hold all the support cords.
I've ordered some ring connectors for the elements and have completed measuring the 20m element directors and reflector, only six more bands to do! By the time I've done the measuring and cutting hopefully the ring connectors will have arrived and I can fit them.
 When weighing the original centre post which was 15lbs, the new centre post is coming in at 3lbs, but I've yet to add the coax connectors for each band. Fingers crossed it will be virtually half the weight of the original centre post, which would considerably lessen the weight of the whole antenna.
(A few days later):
Ok the base plate and spreader arms have been attached, they were all previously measured out so I had no real problems there. I've also added the support cords so the basic shape is now in place. I must admit it's bigger than I thought, so the idea of fitting in a small sized garden puzzles me slightly!
I've measured out the wire elements and as I only target 20, 17,15 and 12 meters at the moment, I'm just adding these I might add 10 and 6 later.
More to follow hopefully over the weekend.

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