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Message-ID: <45C30B1620CA4C5CA65D6DB3D8A1E0F4@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <6DEA7E8987244A48846E44813972D608@TonyLaptop> <1845591504.511262.1277453070420.JavaMail.fmail@mwmweb034> <75F6684803394030B28412B2B11384EC@TonyLaptop>
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Date: Fri, 25 Jun 2010 12:47:48 +0100
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Subject: Re: LF: Antenna wire
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Dear Tony, LF Group,

The most important parameter of an LF vertical antenna is its height, more 
specifically the "effective height", which, for antennas that are a small 
fraction of a wavelength in overall length, is roughly speaking the average 
height of the conductors making up the antenna. Increasing the length has 
secondary benefits, but height has by far the strongest effect on overall 
efficiency. The resistance of the wire will contribute to overall losses, 
but at LF this is relatively low due to the reduced "skin effect" compared 
to higher frequencies. So even fairly thin wire will probably add no more 
than a few ohms to the overall loss resistance, and this will be reduced if 
you go for the parallel 2-wire configuration.

So the main thing is to go for robust, reasonably light weight wire that can 
be put under enough tension to minimise sagging and so reduction of the 
height. I have used the tri-rated switchgear cable favoured by G7NKS for 10 
years now without problems, but I guess any stranded, plastic sheathed cable 
would be about the same. One could split up mains cable to get this quite 
cheaply if specialist suppliers are not convenient. The solid-cored "twin 
and earth" mains cable is probably the cheapest and easiest to strip the 
outer sheathing off, and the inner cores are very robust although obviously 
less flexible. Probably the smallest 1mm^2 gauge would be fine.

I have tried using copper coated MIG welder wire for antennas, but as G3YMC 
says, the coating is too thin and quickly rusts through. There is such a 
thing as "copperweld" wire with a thicker copper cladding, but this is quite 
a specialised thing. Electric fence wire looks tempting, but usually has 
stainless steel strands with a high RF resistance. A lot of the el Cheapo TV 
coax around has a copper-plated steel centre conductor with an outer 
consisting of a few strands of braid with an aluminium foil, and in my 
experience is well worth avoiding for any application!

Cheers, Jim Moritz
73 de M0BMU

----- Original Message ----- 
From: "Tony Baldwin" <ei8jk@o2.ie>
To: <rsgb_lf_group@blacksheep.org>
Sent: Friday, June 25, 2010 10:35 AM
Subject: Re: LF: Antenna wire


Would welding wire do, the CO2 welding wire about 1mm copper coated steel 
wire ?
That I already have a roll of and it's available in Lidl this week.
Tony, EI8JK.