Fellow Experimenters, Frank and Hasan.

I havn't the foggiest idea what you are doing with NEC4 but you should
be aware that, according to Radial_3, there are 3 resonant frequencies
with a single radial at lengths shorter than 10 metres and at a
frequency of 7 MHz.

The propagation velocity is very low. VF = 0.225

Funny unexpected things happen on multi-resonant lines especially when
Zo has a relatively large positive angle. Before you draw any
conclusions about deducing attenuation from your output data you
should take into account the line is -

1/4-wave resonant at 2.4 metres.
1/2-wave resonant at 4.8 metres.
3/4-wave resonant at 7.4 metres.

and at 10 metres it is very near to full-wave resonance. It can be
assumed the far end is open-circuit. Actually it isn't. It behaves
as if it is slightly longer.

It is significant that at 10 metres and 7 MHz, you have concluded that
the radial is about 20dB long. Which approximately agrees with my
program as being the length beyond which there is not much point in
extending it.

But the best way of determining attenuation is to do what I have
suggested - increase radial length in short increments and observe
what happens to radial input impedance. Eventually, Zin will converge
on Zo if it hasn't already done so. I should very much like to know
what Zo is and at what length it occurs. I have to assume NEC4 knows
what it's doing! ;o)
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Reg.