Topband: Skywave vs. Earth Conductivity

[K1FZ-Bruce]

Low band hams are very aware of "sea gain" minimum salt water 
attenuation at low angles. 
The signal will not  produce a perfect circle as the posting shows. 

73
Bruce-K1FZ
www.qsl.net/k1fz/beveragenotes.html

On Fri, 13 Feb 2015 10:35:28 -0500, Bill Whitacre <bw at his.com> wrote:
Perhaps FCC models don't take account of 'sea gain?' ITU models do, as 
I recall. 
>
> Bill Whitacre
> Alexandria, VA
>
> ---
>
> > 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
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