Topband: Skywave vs. Earth Conductivity

[Bill Whitacre]

Perhaps FCC models don't take account of 'sea gain?'  ITU models do, as I recall.

Bill Whitacre
Alexandria, VA

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> On Feb 13, 2015, at 7:43 AM, Richard Fry <rfry at adams.net> wrote:
> 
> From my reading of posts on many "ham" boards, the prevailing thoughts are that the nighttime skywave field intensity received from a vertical monopole is dependent on earth conductivity -- as well as on frequency, radiated power, path length, and atmospheric conditions.
> 
> The plot linked below applies to the skywave from WFAN, a New York City station on 660 kHz using 50 kW/24-7 and an omni vertical radiator.  It shows the FCC 0.25 mV/m RMS contour for the skywave received 50% of the time, six hours after sunset in NYC.
> 
> There is no visible/useful difference in the radius to that contour over the ocean than over the land.
> 
> This plot doesn't appear to be supported by a NEC far-field analysis of such a system -- on which (apparently) most hams base their conclusions about the skywave coverage potential of a vertical monopole for given values of earth conductivity.
> 
> One reason for this difference is that NEC far-field calculations apply to ~infinite distances over a flat ground plane.
> 
> Just wondering what thoughts others have on this subject.
> 
> http://s20.postimg.org/f1z0o2e7h/WFAN_Skywave.gif
> 
> R. Fry, CPBE