At TX5D (FO-A), I was able to instant A/B a 15m vertical (two elevated
radials) at high tide line vs a crankIR tuned on 15m about 70' from high
tide. US stations (5k to 7k km) reported 1 to 2 S unit improvements
with the antenna nearer to the lagoon salt water. Received signals were
at least that much improved.
There is a NEC4 analysis of two semicircular grounds, one salt water the
other average earth which verifies the improvement. Not sure where it
is published though. I think this model shows the closer to salt water
the better and less than 1/2wl is where the improvement is significant.
Somewhere around 1.5wl there is no improvement.
Grant KZ1W
On 2/13/2015 7:53 AM, K1FZ-Bruce wrote:
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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