Phil Kane writes:

On Thu, 2 Oct 2008 16:44:22 EDT, Michael Coslo wrote:

Now a simpler way to do all this, and much less dangerous, is to use
maps like the one at:

http://www.fcc.gov/mb/audio/m3/index.html

Ah yes, the venerable M3 map. It is only an approximation, and for
real-life stuff it isn't used any more, supplanted by real ground
conductivity measurements.

How much would you get out of plotting how impedance changes as you
lower the antenna?

Jon LA4RT