I did some modeling of radials with elevated radials after 3 "on the
beach" DXpeditions. QST said they will publish it this year, sometime.
Rudy N6LF has done a lot of modeling of elevated radials see
antennasbyn6lf.com and his QEX articles.
From my modeling: There is quite a bit of improvement in low angle gain
(<15 d) for verticals with elevated radials within 1/4 wavelength of the
tide line. As far back as one wavelength there is some good low angle
(<7 d) gain improvement. Two elevated radials parallel to the tide line
work well. Further back than 1 wl, the pattern reverts to a normal
vertical so lots of ground radials or 8+ elevated radials yield normal
vertical patterns. Neither has the gain of a near salt water vertical
below 10 d.
The ground conductivity of an atoll is an interesting question, at what
depth is there salt water? For wet sand the conductivity is probably
about 1/4 that of the sea, still great at 1 S/m vs soil. So over wet
sand elevated radials are FB, but over several feet of coral to salt
water ?? I think subsurface fresh water on a true atoll is pretty rare
and full salt water incursion is the norm.
It is surprising to me that K5P isn't stronger here near Seattle, that
has me wondering where they were required to put their antennas. The
tide line separation may explain why they are reported stronger on 160
than 80. Web photos of Palmyra show what appear to be a big tidal
range and an atoll becoming an island. Tide cycles might be involved in
how well they get out.
Grant KZ1W
On 1/16/2016 15:54 PM, Mike Waters wrote:
Hi Art,
Whether or not elevated radials would help K5P, what you stated is NOT pure
speculation! :-)
Generally speaking, it is well-established that we can use far fewer
elevated radials under a vertical than ground mounted radials, for the same
efficiency.
73, Mike
www.w0btu.com
On Sat, Jan 16, 2016 at 5:22 PM, Art Snapper <art@nk8x.net> wrote:
I wonder how good the ground conductivity is on an atoll? Perhaps
elevating the radials would help.
My $0.02 of pure speculation.
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