Topband: Testing Soil Conductivity

[w8av]

The FCC M-3 Map, although used for predicting coverage and interference for AM broadcast stations at the application stage, uses theoretical soil conductivity data from the 1950's.  Although it will get you somewhat in the ballpark, the actual conductivity can vary a good deal from actual measured values.  For example, The M-3 map predicts the ground conductivity for North Central Ohio as 8 mS/m.  In the summer months I have measured values as low as 4 mS/m and no higher than 6 mS/m in the winter months.  In Western Ohio the theoretical conductivity is predicted as 15 mS/m and the measured values agree closely with the theoretical ones.  So the map is an estimate which may or may not be totally accurate.

Since the FCC now requires most applications to be filed electronically, you may be able to obtain relatively recent and more accurate measured conductivity values from an AM broadcast 301 application filed for a station in your area (a 301 application is an application for a construction permit for an AM Broadcast Station).  If you do a search of the FCC web site for AM broadcast applications in your area, you may be able to find the measured values in pdf attachments to the application.  That might give you some insight on ground conductivity values in you area.  The applications are all a matter of public record so you should have no trouble accessing and viewing them.

73.................de Goose, W8AV