On 3/8/2015 7:21 PM, Brian Reay wrote:

There is a world atlas of conductivity which is on the web, I can't
recall the URL, but it is worth looking out. The various seas and oceans
do vary, I recall the Baltic being less conductive for example.
Likewise, some of the patterns in the various countries are rather
intriguing. Some areas you would expect to be conductive are not. I
assume due to local rock formations etc.

I've been lurking in this thread and it reminded me of a time many years
ago when I was working on a receiver setup. A colleague gave me a book
with an equation for signal strength of a signal in the cell phone
frequency range in various terrestrial environments. I had a little
trouble accepting an arbitrary equation that wasn't at least close to
the typical 1/r^2 formula in free space. I seem to recall there was no
1/r^2 term at all rather it was more like a linear or maybe had a
rlog(r) term.

In any event, no one could explain where the equation came from. I
suppose it was an empirical equation rather than something derived from
theory. Ignoring waves bounced off the upper atmosphere, I assume the
earth acts to help focus the signal and strengthen it close to the ground?

--

Rick