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@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@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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