[TowerTalk] Ground radials/elevated radials

[Jim Lux]

----- Original Message -----
From: "Yo3ctk" <yo3ctk at alltrom.ro>
To: "Tom Rauch" <w8ji at contesting.com>; <towertalk at contesting.com>
Sent: Friday, October 22, 2004 4:50 AM
Subject: Re: [TowerTalk] Ground radials/elevated radials


> The same would hold true for elevated radials?

No.
Well... the advice of the more radials the better is sound, but when you
start looking for resonant lengths, etc. it gets much trickier.

When they were validating NEC-4, a fair amount of research was done at LLNL
(you can search their online archives to get the reports) on things like on
elevated radials over deteriorated buried radials, etc.  The upshot is that
NEC4 (and similar modeling codes) does a great job modeling, IF, and only
if, you've got a good representation of the earth properties, which
unfortunately, is very hard to come by.

If you don't know the earth properties, then modeling the radials as
straight wires above uniform ground is about as realistic as using that
model to represent radials laid over bushes and trees haphazardly. (the idea
being that bushes and trees cause small scale variations in the dielectric
properties around the antenna).


>
> I am designing a 4-square for 80m. Full size verticals. Comteq
> phasing/switching unit. But I need elevated radials for practical reasons
> (the land below is used for small-size agriculture). I am not sure how
many
> and how long radials are needed for each antenna. I am not after the
> ultimate system, only one with decent results.
>
> Thank you for any suggestion. Best regards,
>
> 73 de Mike, YO3CTK (YR7M in contests)
>
> ----- Original Message -----
> From: "Tom Rauch" <w8ji at contesting.com>
>
> > No. Radials needs to be as many as long and as straight and
> > evenly spaced as possible. If they are close to ground or on
> > ground, you need 20-30 0.2 wavelength long to have a really
> > good ground. About 50 or 60 radials is nearly perfect.