Fw: Topband: Measuring ground conductivity

[Sam Dellit]

 g'day all

 i am doubtful whether ground conductivity can be measured accurately
by the method you describe as a low dipole & certainly any extrapolation
to 160m would be questionable.

 i think the tried and true methods are generally the best. for am broadcast
antennas the regulatory authorities require ascertainment of actual radiated
power
and related characteristics. we call the process a "cmf run" in australia
and i believe it is a "proof of performance" in the usa.

 the principal component of this exercise is carefully selecting a dozen or
so
good measurement locations on a single radial from the antenna and recording
the measured field strength. these measurements can then be applied to
graphs of
calculated field strength variations with distance. the process yields both
effective radiated power (unattenuated field strength in mV/m at one mile or
cymomotive force - unattenuated field strength in mV/m at one kilometre) and
an excellent estimate of the ground conductivity along the radial.

 where ground conductivity is homogeneous the process is straight forward
but where there are inhomogenieties rapid escalation in complexity occurs.
ground conductivity can vary with frequency if there is significant
stratification
of layers of varying ground conductivity, due mainly to the variation in
penetration depth. i think that the nab engineering handbook has a lot of
information
on this topic

 i have minimal experiece with estimating ground conductivity in a small
local area

 hth

 73s

 sam dellit   vk4zss



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