Rick,
What you are saying is correct a short vertical requires a lower ground
resistance for optimal performance and thus a more extensive number of long
radials. Otherwise there is further compromise. I think the confusion
may be that if one only has a small number of ground radials say sixteen
then the optimal electrical length is only 0.1 electrical wavelength while
if one has 120 radials the length increases to 0.4 electrical wavelength.
This is the electrical wavelength though and not the physical length of the
radials. The proximity of soil changes the velocity factor so that in fact
the radials are considerable shorter. Say 110 feet for 120 ground mounted
radials. The absolute length is dependent on the characteristics of your
soil. This is not so terribly critical though so if one uses 100 to 130
feet lengths with 120 radials then there is less than say 0.5 dB in it.
Now please do not hold my feet to the fire. Read the K9YC article it is
good.
Also as previously stated it is not necessary that all radials be the
same length. For many this is not possible. Compromise is called for
with some degradation in performance.
I am also learning and open to correction. The forum in a learning
experience and in trying to state ones understanding it is possible to learn
and sometimes this comes about by correction.
73 Doug EI2CN
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
Richard (Rick) Karlquist
Sent: 29 February 2016 23:02
To: jimlux; towertalk@contesting.com
Subject: Re: [TowerTalk] Radial question
On 2/29/2016 2:29 PM, jimlux wrote:
>
> So, if you had a 5-10 meter tall radiator, being used on 80m or 160m,
> there's not a lot to be gained by going longer than 15-20 meters for the
> radials.
>
This often heard concept makes intuitive sense. Kind of
like how the roots of a tree should be of a length related
to the tree height or width.
However, it simply isn't true. Actually, the opposite
is true. Jerry Sevick, W2FMI, wrote an article for QST
a long time ago that famously had a photo of a 40 meter
vertical that was something like 7 feet high, with a top
hat, but worked over a huge radial field. The thing
that was funny about the photo was that the antenna was
made of a clothes dryer with metal arms that served as
the top hat and the pole was the radiator. The concept
was that the less you have in the air, the more you need
on the ground. Jerry did seem to know what he was talking
about.
The "capture area" of a short vertical is nearly the same
as that of a 1/4 wave vertical, no matter how small it is
(at least in the absence of losses). Thus there is no
justification for shortchanging it on radials.
Rick N6RK
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