Reg,

I certainly don't think you are trolling. You have aroused a very
interesting discussion. I'm absolutely fascinated. The issue isn't whether
Tom can detect the current at a point beyond your description. The point is
will that current be quite a bit larger than the 20 dB down your approach
predicts.

This is getting pretty simple...either the current is or isn't substantial
beyond the wire lengths you describe. If it isn't, you have hit on
something big. If it is, then the model you are using or the application of
that model is in error. I'm just trying to learn which of these two cases is
true. I find your analysis breathtakingly interesting. It's just hard to
resolve the apparent contradictions....fun nevertheless! Thanks again.

....hasan, N0AN
"Reg Edwards" wrote in message
...
Hasan et al,

Tom says current can be detected in radials well beyond the 20dB
attenuation limit. This is easily explained.

The total current flowing in the system at a distance is in the soil
due to its far greater cross-sectional area. Especially when soil
resistivity is low. Nothing in particular happens in the soil at the
end of the 20dB limit.

The small current in a radial is INDUCED in it by the relatively
larger total current flowing in the soil in parallel with it. The
radial current is NOT generated by the voltage at its input. Its high
attenuation isolates it from its input.

What current flows in a radial has a progressively less effect on the
total current (which is what matters) as distance increases.
Eventually, it doesn't matter whether the radial is there or not.

The limit is reached when the radial input impedance converges on Zo,
the radial's characteristic impedance. This occurs when radial
attenuation is around 18 or 20dB. Beyond that distance the current
flowing in the ground carries on, as usual, unaffected whether the
radial is there or not.

Resonant effects, small peaks and troughs in the impedance-frequency
curve, also die away at the 20dB or even lower limit. There's not much
left even at 14dB.

Radial attenuation increases rapidly with frequency. So shorter
radials can be used at 14 MHz than at 1.9 MHz. When 30 MHz is the
lowest frequency of use, and soil resistivity is high, a dipole,
without radials, is more likely to be used than a vertical.

(Comment: I guessed correctly I would be accused of trolling when I
introduced the subject of radials as transmission lines.)
----
Reg, G4FGQ.