"hasan schiers" wrote in message
...
I don't know about boundary conditions, but when I use this program
to
evaluate the following system:

3.62 Mhz, 18.3 meter height (simulating an inverted L with 25.4 ohms
Rrad)

Resistivity 25, Permittivity 25

2mm radials, 4mm antenna wire, radials 1 mm depth (actually #14
insulated
wire, stapled to the lawn and sinking in gradually)

..it shows my predicted efficiency with (26) 50' long radials to be
about
90%.

My measurements indicated I am getting about 88%. Pretty good
agreement.

=========================================
Yes Hasan, good agreement. How did you determine efficiency to THAT
degree of accuracy?
=========================================
What causes me to cringe, is that the program shows that I can
reduce the
length of my radials from 16.1 meters to a little over 4 meters
without
losing ANY significant efficiency. Given everything else I've read
over the
years, that just seems to be way too good to be true.
=========================================
You've been reading books and magazines about rules-of-thumb written
by old-wives. At 3.62 MHz and a radial length of 16 metres the
attenuation approaches 100 decibels. So there's no current flowing in
the radials beyond 5 metres. You can remove the excess 12 metres.
They are not doing anything. What small current density there is
beyond 5 metres is all flowing in the soil. The cross-sectional area
of the soil carries the small current just as well as the radials.
=========================================
Now, I suppose I could rip up my 26 radials and shorten them all to
about 5
meters and re-measure my efficiency, but that's a LOT of work (and
it's 97
degrees out with a dew point in the mid 70's). Not going to happen.

Here's the kicker... I have 1000' of remaining wire to put down (and
I am
going to add it). If this value of 4 or 5 meters (15 feet, let's
say) is
even remotely correct, I can put down 66 more radials (although they
would
be interlaced with the existing 26 longer ones of 50' each).

Using my initial length of 50', I can put down 20 more radials,
giving me a
total of 46 radials 50' long.
==========================================
Yes. Use the program to calculate efficiency with the extra 20
radials. Assume all the radials are 5 metres long. But you may not
think the meagre 3% or 0.13dB in efficiency is worth all the labour
and back-ache. By now you are beginning to appreciate how useful the
program is.
==========================================

Reg, you program seems to be telling me that I would get the maximum
benefit
by putting in 66 more radials approximately 15' long, and that
installing
them at 50' would be wasting 35' of wire per radial, and reducing
radial
coverage as well.

So...what should I do:

1. Add 66 greatly shortened radials (accepting Reg's program as
correct)

or

2. Add 20 radials, maintaining my 50' length that I originally used.

I look forward to comments.
==========================================

Hasan, if I were you I would lay some extra short radials between the
existing long radials - and get some Sloan's liniment to be massaged
into my back. But the increase in efficiency would be un-measurable.
You are fortunate to have very low soil resistivity. Mine is about 70
ohm-metres and for years on the 160m band I have had 7 radials about 3
metres long plus an incoming lead water pipe.
----
Reg, G4FGQ