[TowerTalk] Ground radials- the long and short of it

Jim Lux jimlux at earthlink.net
Fri Oct 22 10:18:26 EDT 2004


Buried radials are basically a means to improve the conductivity of the soil
under the antenna, not as a resonant part of the antenna (if nothing else,
the resonant length in soil would be difficult to determine).  Therefore,
the basic idea is as many and as long as you can get.

Where the disputes will arise is determining the point of "diminishing
returns".

There have been a fair number of measurements, and even more theoretical
modeling of this to try and determine what the "right" answer is, mostly to
no avail.

The primary reason (I suspect) for deviation between ham measurements and
models is that virtually all models make the assumption that the ground
properties are uniform, which they are almost certainly not (except for a
few lucky hams, and even there, there are probably significant
inhomogeneities).

If you really wanted an accurate model of something close to the ground, you
need to measure the soil electromagnetic properties to the same sort of
accuracy as you use to defining the physical structure.  And even if  you
had those measurements, most antenna modeling codes don't deal with
non-uniform soil properties (i.e. there's no way to enter them).

So you fall back on a sort of qualititive approach.. no matter what the
modeling approach, more radials are better.

Jim, W6RMK

----- Original Message -----
From: "Scott Fike" <kc0bus at hotmail.com>
To: <towertalk at contesting.com>
Sent: Thursday, October 21, 2004 11:30 PM
Subject: [TowerTalk] Ground radials- the long and short of it


> Pertaining to a ground-mounted vertical antenna with buried radials a few
> inches below the surface of the grass:
>
>   Do ground radials have to be electrically the same length as the main
> vertical radiator element?
>
>   Example: Take a 1/4 wave 80 meter hamstick stuck vertically in the
ground.
> An 80 meter hamstick is physically about 6' tall but has about 60' of wire
> wound hellicaly around its 6' core insulator rod. Would it be better to
make
> my ground radials using hamsticks (with their 60' of wire but physically
> still 6' long overall) or can I use 6' pieces of wire to match the
hamsticks
> physical overall length or should one string out 60' radials?
>
>   Some books I've read say:  ".... make the ground radials 1/4 wavelength
> long to match the main 1/4 wavelength long vertical element". Other books
> and sources say: "..... just make the ground radials as long as you can to
> fit in the availible space in your yard".
>
> Scott, KC0BUS
>
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