Topband: Monopole Elev Pattern w.r.t. Earth Conductivity

[Shoppa, Tim]

OK I'm confused.

All the AM radio stations registered with FCC publish curves showing 2.5, 0.5, and 0.15 mV/m contours. I'm assuming these are field strengths on the ground e.g. low angles. http://radio-locator.com/cgi-bin/pat?call=WGN&service=AM&status=L&hours=U

I always thought that these were based on models of local terrain/ground conductivity and antenna patterns with some cross-checking against real measurements (E.g. selective voltmeters).

Many of the AM stations have very "interesting" coverage patterns due to local and distant variations in ground conductivity as well as beam patterns formed by phasing multiple towers so these patterns on not done just by seat-of-the-pants.

Is 160M so bizarre that the same electromagnetic principles (used for half a century to carve up AM frequency allocations across the US and Canada) are not applicable to finding field strength on the ground for 160M ham stuff?

Tim N3QE