This is fascinating stuff. My 160 meter vertical is less than 2
wavelengths away from the Great Pond Bay and the salt water lagoon
inside which includes a floodplain of very brackish water. This is
proven my taste and by the fact that there are plenty of mangroves
there. Before I knew any better I ran 1000' coax and then a 600'
Beverage from on side of the salt flat muck to a post on the other using
an existing series of fence posts. The results were horrible and my
inland Beverages over a former hay field worked but the salt pond
beverage did not. All I can say that to a moral certainty that whatever
that proves it proves.
Herb Schoenbohm, KV4FZ
On 4/2/2015 3:59 PM, Grant Saviers wrote:
Since this thread continues, I thought I would share some EZNEC Pro/4
modeling results I have submitted for publication to QEX, with a focus
on "verticals on the beach" for DXpeditions. EZNEC Pro4 can segment
ground along a line into two arbitrary ground properties, in my
modeling 4 S/m, 80 for salt water and 0.005 S/m,13 for land. W3LPL's
and other's guidance is roughly consistent my modeling of a vertical
at various separations from the tide line.
The brief summary of modeling results is there is significant benefit
at elevation angles <20 degrees towards the salt water IF the antenna
is less than 0.7 wavelengths (WL) from the tide line. The pattern is
asymmetrical in azimuth as a result, favoring the salt water. The -2db
azimuth pattern at 5 degrees elevation is 140 degrees wide at peak
4.5dbi gain towards the water when the vertical is 0.3 WL from the
tide line, with 2 radials elevated 0.025 WL. In this case the F/B is
11 db. Around 0.45 WL from the tide line the elevation gain -2db
point starts to fall below 20 degrees and continues to fall as
separation is increased. Since my objective was to better understand
the tradeoffs for DXpeditions, only 1 or 2 elevated radials were
modeled and additional radials did not enhance seaward performance.
In this case, elevating the radials helps the peak gain, about 0.15 WL
is optimal. Further than 1 WL from the tide line, there is
essentially no low angle gain benefit from the sea and the vertical
pattern is whatever you have as ground + radials. The results for
azimuth and elevation gain and pattern showed no fractional wavelength
peaking, the values all smoothly trend out to more than 1 wavelength
from the tideline.
These are only gain results, so the seaward path may have much lower
skip and/or ground wave losses.
Grant KZ1W
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