Alexander RA9MB wrote:
> Fore large distanses i expect behaviour E ~ 1/sqrt(d).

This would be the most straightforward explanation
for the high signal strength.

The signal expands with 1/r^2 power density and 1/r field
strength until it is constrained by the Earth-ionosphere
cavity, at say r = 100km.   Thereafter, expansion is
1/r power density and 1/sqrt(r) field strength.

For long distances, we can just assume 1/sqrt(r) field
strength.

We have then B = sqrt( 9.5e-21 * ERP/r) for a daytime
D-layer at a height of 70km.

For 1mW ERP over 850km, that gives 3.3fT which is a much
better estimate than the 1/r^2.  With multi-path interference,
it could vary between zero and twice that figure.

For conservation of energy, it cannot be higher than
that, so that gives an upper bound.

Then there must be the exponential factor for attenuation...
--
Paul Nicholson
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