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

Subject: Re: Topband: Monopole Elev Pattern w.r.t. Earth Conductivity
From: "Shoppa, Tim" <tshoppa@wmata.com>
Date: Thu, 25 Oct 2012 14:33:41 +0000
List-post: <topband@contesting.com">mailto:topband@contesting.com>
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
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