[TowerTalk] FW: low band antenna without good ground

[Ian White GM3SEK]

Jim Lux wrote:
>On 9/25/11 9:41 AM, Kevin Normoyle wrote:
>>
>>>  From ON4UN's Low-Band DXing regarding ground enhancements using mesh
>> screening...   "Steel is a very poor conductor at RF"
>>
>>
>> Looking at VK1OD's table here, zinc is pretty good
>> http://vk1od.net/antenna/conductors/loss.htm
>>
>> so zinc-plated steel, or Al would be fine,


The RF conductivity of the steel is irrelevant, because its high 
magnetic permeability forces almost all the RF current outward into the 
skin of zinc (even if the thickness of the plating is less than the 
normal skin depth in solid zinc.)  The steel is then acting only as a 
mechanical support for the 'tube' of zinc plating which is where almost 
all of the RF current flows.

This means that the RF conductivity of galvanized wire is determined 
almost entirely by the diameter of the wire and the thickness of the 
zinc plating. Good industrial-quality stock fencing scores well on both 
of those points, and then the mesh construction provides multiple, 
diversified current paths which further improve the conductivity.



>> it's just the corrosion issues.?
>>
>
>I think so.  It sort of depends on a whole cost/benefit analysis... If
>you're rolling out wires for a weekend or a couple weeks, cheap and
>light might be the ticket (go aluminum!).  If you're installing a ground
>field for your 160m full wavelength vertical to reduce losses so you can
>beat the guys operating in the middle of a salt marsh for the Stew Perry
>for the next 20 years, then copper might be a better choice.
>
>ANd the corrosion thing will be highly site specific.  If you're out in
>the desert (where soil conductivity is really, really low), practically
>anything will help.  If you're in that salt marsh, galvanized fence
>wire's probably not a good choice.

At this QTH, where I can *taste* the salt on my antennas, the galvanized 
wire mesh is lasting just fine. If it gives me another 5 years, it will 
have been a very good investment and I'll do exactly the same again.



-- 

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek