Having some time ago come to the conclusion that (despite being great as a portable) my MP1 is unsuitable for my back garden, where the QRM makes it virtually unusable, I have decided that the time is right to make my own antenna.
At home, I use 20m more than anything else, so a “simple” wire dipole for 20m is the obvious choice.
Searching the inter-web, I know exactly how long each leg needs to be (yes, I know to cut long and tune) but what no-one ever seems to mention is the wire type.
Should I use:
plain copper or copper-clad steel
solid or stranded
bare or enamelled (or other insulation)
And what guage wire should I use?
I know a number of you build your own, so any opinions are welcome
Hard drawn copper is one choice. Hard drawn means it wont stretch under its own weight. This is single strand and can be quite thick. Soft drawn will stretch eventually.
You can use stranded wire but it can become noisy. This can happen when the wire moves and the strands are partially insulated from each other with dirt/oxidisation. As they move and rub there can be crackles.
If you use plastic covered wire then the velocity factor will change and the lengths will different to what you expect.
The gauge depends on your wallet, what you can scrounge, how invisible you want and how often you want to fix it.
The important point is there is no right answer.
Investing in some form of antenna analyser is money well spent in my book. You don’t need one to make effective aerials, just a bit of nouse and practice. But having one can simplify things no end. Also it’s interesting to play about and see the effect directly on the analyser.
(Now 6hrs non-stop heavy snow with 9cms fallen so far.)
Andy
MM0FMF
In reply to M6ADB:
This is just my opinion…and I am sure some venerable sage will be along soon to tell you something different…but here goes:
I prefer to spend as little money as possible, as I usually find that my first (second/third) version usually ends up in the bin as I tend to modify as I go.
This is one of my main delights in the hobby - designing, changing, redesigning and loosing ones temper when playing with arials.
I tend to go to the local electrical wholesalers and buy a 50/100m drum of 1.0 or 1.5mm 6491X singles cable. This is stranded and copper and comes in a variety of coloured insulation.
I prefer to buy it in grey as it tends to dissapear when up in the air.
Usually 1.0mm is plenty.
Best thing is to try a few designs and materials…you’ll find something that you like.
Yep, there’s one thing of which you can be almost certain; you’ll end up tinkering with it, tuning it, taking it down and trying something different, and sooner or later finding it’s gone and done something un-expected…
My external fan-dipole’s suffered a noticable drop in its points of resonance in the last few weeks. Something to do with the cold, the wet, the snow, the fox, and who knows what else, I guess…
In reply to M6LEP:
For my wire dipoles i have used 1.0mm sq pvc coated multistranded cable. But if at all possible avoid DIY shops and the like, go to an electrical trade counter, i picked up a 100m reel for less than £10
In reply to M6ADB:
My favourite antenna wire is of the DX WIRE type. It has a steel core with a layer of copper. My ant has been up for several years without any problems and it is nearly invisible. Just check the net for DX WIRE.
Good luck Martin df3mc
In reply to M6ADB:
Hello Andrew
I have G6WRW pattern inverted vee dipole up in the garden in insulated flexweave / speaker cable [article now only available on [ http://www.moosedata.com/g6wrw/hfdipole.pdf ]and it’s fine with broadband usable tuning across 3.5 and 7 MHz. There’s a lot of electrical noise apparent so I’m reading the Elimination of Electrical Noise by Dan Pinnock book for some more clues on a course of action.
My next experiment is to build a long wire horizontal loop rather like G3MGW’s article in RADCOM May 2009. My clubmates in Telford & DARS report noise-free reception of wanted signals. An article by M0PNN in the November 2009 edition of the club newsletter http://www.tdars.org/html/NewsLetters.html ]covers his horizontal loop and new balun.
You could build the VK5JST antenna analyser kit, which represents very good value for money for £75, to help you with your experimentation. The vendor if asked nicely will word the description on the packet favourably so Royal Mail doesn’t charge £15. I like mine a great deal. Super project for 2E0 exam too.
It is scalable to 20m, and very lightweight. The Aluminium welding wire I use came from a welding supply place in Hull, it was a 15Kg drum and quite expensive - though I do use it for welding too… B and Q sell the same stuff in small drums for about £15.
