Topband: [Bulk] Re: Skywave vs. Earth Conductivity

[Grant Saviers]

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 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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