Topband: insulated vs:bare radial wires

[Gene Smar]

Todd:

     I use insulated radials for my (now removed) inverted L and shunt-fed 
tower on 160M simply because insulated wire lasts longer in my back yard 
than does bare copper.  My first antenna at this QTH (outside Washington, 
DC) was a Hygain 18AVQ all-band vertical for 80-10M.  I installed about a 
dozen #20 gauge bare copper -clad steel radials and connected them DIRECTLY 
to the aluminum mounting bracket of the antenna.  (No anti-corrosion 
compound or stainless steel to prevent galvanic corrosion, but I digress.)

     The antenna sucked, i.e., it worked equally poorly in all directions. 
I worked a bit of DX with it but only during the sunspot peaks when even a 
loaded rain gutter might have been as efficient.  When I dug in the vicinity 
of the vertical's base to begin excavation for my tower in the same spot, I 
found nothing was left of the copper-clad wire.  It had all gone back to 
Mother Earth in the years it was outside.

     Since then I've used insulated wire for the above reason; and scrap 
insulated wire is cheap.

     Your theory on using lots of copper to collect antenna currents 
underneath the vertical element is pretty much correct, from what I have 
learned here on Topband.  However, as others here have said, there is a 
point of diminishing returns beyond which you get less and less improvement 
in antenna efficiency for the same amount of added copper radials.  The 
general concensus here is that beyond about fifty to sixty feet of in-ground 
radial wire you would be better off adding more radials than making them 
longer.  This is for lowband operation (160 - 40M.)

     The ARRL published an article in QST (June, 1985, N2MF) in which the 
author used NEC to calculate the theoretical perfomance of more vs longer 
radials for vertical monopoles.  The results showed an obvious flattening 
out of the efficiency curve (as measured by calculated gain of the antenna 
plus ground system) as you added radials, or as their lengths increased.

     BOTTOM LINE:  If you have only so much wire, or space, for your radial 
network, you can determine an optimum number and length of radials for use 
with your monopole vertical.


73 de
Gene Smar  AD3F


----- Original Message ----- 
From: "Tod -ID" <tod at k0to.us>
To: <topband at contesting.com>
Sent: Friday, December 04, 2009 10:21 AM
Subject: Re: Topband: insulated vs:bare radial wires


> I guess I have the wrong idea about how the radials of a vertical work. 
> For
> some reason I thought that they operated as a 'screen' that kept the 
> return
> currents out of the ground enough so that the "ground" losses were less.
>
> If my flawed view of this happened to be true, then the more radials the
> better [although at some point the incremental difference becomes 
> difficult
> to measure]. It might also mean that insulated is better than 
> non-insulated
> since there would be no leakage current between the ground and the wire.
> That 'leakage' current probably is so trivial that no one notices it and
> the practical result is that there is no significant electrical difference
> between insulated and non-insulated.
>
>
> Since I am speculating here, if I am lucky someone will either confirm my
> conjecture is correct or advise me about how things really work.
>
> I know that there are at least two guys on this reflector who, I think, 
> know
> pretty well how the radials work.
>
> Tod, K0TO
>