> Hi Rik isn't it more likely to be the case that these low antennas are much
more dependent on ground conditions, which are not modelled very well 


Highly likely! This is one of the things that has become painfully obvious to 
those of us interested in cave radio.

To add to the problems, there will be rock at some depth under the ground. This 
depth can vary enormously: soil over limestone is probably a metre or less deep 
(very much a guess); in parts of southern England, on London Clay, hard rock 
can be tens or even a hundred metres down. Nor is there any reason to suppose 
that the soil/rock boundary is either level or smooth. 

The conductivities of soil and rock presumably matter, and may vary from place 
to place. They will certainly vary with the recent rainfall.

So you may be dealing with a two-layer problem with a top layer of unknown and 
possibly varying thickness, and two layers of unknown and varying conductivity. 
Apart from that, modelling it is child's play!

73,
Chris Trayner, G4OKW


-----------------------------
Dr Chris Trayner
School of Electronic & Electrical Engineering,
The University of Leeds,
Leeds LS2 9JT, United Kingdom
Tel: +44 113 34 32053
Fax: +44 113 34 32032

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